forming part of a bundle, have angled outlines when they are
completely surrounded by other bast fibres; but when they occur on
the outer part of the bundle, and when in contact with parenchyma or
other cortical cells, they are partly angled and partly undulated in
outline.
In the bast fibres the pores are placed at right angles to the length
of the fibre. The side walls show the length of the pore (Plate 24,
Fig. 3); while the upper or lower wall shows the outline, which is
circular, and the pore, which is very minute.
Most bast fibres have no cell contents. In some cases, however,
starch occurs, as in the bast fibres of rubus.
The color of the bast fibres varies, being colorless, as in Ceylon
cinnamon; or yellowish-white, as in echinacea; or bright yellow, as
in bayberry bark.
Bast fibres retain their living-cell contents until fully developed;
then they die and function largely in a mechanical way.
The walls of bast fibres are composed of cellulose or of lignin. Most
of the bast fibres occurring in the medicinal plants give a strong
lignin reaction.
WOOD FIBRES
=Wood fibres= always occur in cross-sections associated with vessels
and wood parenchyma, from which they are distinguished by their
thicker walls, smaller diameter, and by the nature of the pores,
which are usually oblique and fewer in number than the pores in the
walls of wood parenchyma, and different in form from the pores of
vessels.
The wood fibre on cross-section (Plate 105, Fig. 4) shows an
angled outline, except in the case of the fibres bordering the
pith-parenchyma, etc., in which case they are rounded on their outer
surface, but angled at the points in contact with other fibres. The
pore of wood fibres is one of the main characteristics which enable
one to distinguish the wood fibres from bast fibres.
The pores are slanting or strongly oblique (Plate 28, Fig. 2),
and they show for their entire length on the broadest part of the
wall--_i.e._, the upper or the lower surface--while in the side wall
they are oblique; but they are not so distinct as they are on the
broad part of the wall.
Frequently the pores appear crossed when the upper and the lower wall
are in focus, because the pores are spirally arranged, and the pore
on the under wall throws a shadow across the pore on the upper wall,
or _vice versa_.
Wood fibres always occur in a broken condition (Plate 28, Fig. 1) in
powdered drugs. These broken fibres usually occur both singly and in
groups in a given powder.
The color of wood fibres varies greatly in the different medicinal
woods. Fragments of wood are usually adhering to witch-hazel, black
haw, and other medicinal barks. In each of these cases the wood
fibres are nearly colorless. In barberry bark adhering fragments of
wood and the individual fibres are greenish-yellow. The wood fibres
of santalum album are whitish-brown; of quassia, whitish-yellow; of
logwood and santalum rubrum, red.
[Illustration: PLATE 28
WOOD FIBRES
1. White sandalwood (_Santalum album_, L.).
2. Quassia wood (_Picræna excelsa_, [Swartz] Lindl.).
3. Logwood with crystals (_Hæmatoxylon campechianum_, L.).
4. Black haw root (_Viburnum prunifolium_, L.).]
Some wood fibres function as storage cells. In quassia the wood
fibres frequently contain storage starch. The wood fibres of logwood
and red saunders contain coloring substances, which are partially in
the cell cavity and partially in the cell wall.
The walls of wood are composed largely of lignin.
COLLENCHYMA CELLS
=Collenchyma cells= form the principal medicinal tissue of stems of
herbs, petioles of leaves, etc. In certain herbs the collenchyma
forms several of the outer layers of the cortex of the stem. In
motherwort, horehound, and in catnip the collenchyma cells occur
chiefly at the angles of the stem. In motherwort (Plate 29, Fig.
B) there are twelve bundles, one large bundle at each of the four
angles, and two small bundles, one on either side of the large
bundle. In catnip (Plate 29, Fig. A) there are four large masses, one
at each angle of the stem.
Collenchyma cells differ from parenchyma cells in a number of
ways: first, the cell cavity is smaller; secondly, the walls are
thicker, the greater amount of thickening being at the angles of the
cells--that is, the part of the cell wall which is opposite the usual
intercellular space of parenchyma cells, while the wall common to
two adjoining cells usually remains unthickened. In horehound stem
(Plate 30, Fig. 2) the thickening is so great at the angles that no
intercellular space remains. In the side column of motherwort stem
(Plate 30, Fig. 1) the thickening between the cells has taken place
to such an extent that the cell cavities become greatly separated and
arranged in parallel concentric rows.
The collenchyma of the outer angle of motherwort stem (Plate 30, Fig.
3) is greatly thickened at the angles. There are no intercellular
spaces between the cells, and cell cavity is usually angled in
outline instead of circular, as in the cells of horehound. In certain
plants intercellular spaces occur between the cells, and the walls
are striated instead of being non-striated, as in the stems of
horehound, motherwort, and catnip.
[Illustration: PLATE 29
_A._ Diagrammatic sketch of the cross-section of catnip stem
(_Nepeta cataria_, L.). 1. Collenchyma occurring at the four angles
of the stem.
_B._ Diagrammatic sketch of the cross-section of motherwort stem
(_Leonurus cardiaca_, L.). 1, 2, 3. Twelve masses of collenchyma
tissue occurring at the four sides of the stem.]
[Illustration: PLATE 30
COLLENCHYMA CELLS
1. Cross-section of a side column of the collenchyma of motherwort
stem (_Leonurus cardiaca_, L.).
2. Cross-section of the collenchyma of horehound stem (_Marrubium
vulgare_, L.).
3. Cross-section of the collenchyma of the outer angle of
motherwort stem.]
Collenchyma cells retain their living contents at maturity. Many
collenchyma cells, particularly of the outer layers of bark and the
collenchyma of the stems of herbs, contain chlorophyll.
The walls of collenchyma consist of cellulose.
STONE CELLS
=Stone cells=, like bast fibres, are branched or non-branched. Each
group is then separated into subgroups according to wall structure
(whether striated, or pitted and striated, etc.), thickness of wall
and of cell cavity, color of wall and of cell contents, absence of
color and of cell contents, etc.
BRANCHED STONE CELLS
=Branched stone cells= occur in a number of drugs. In witch-hazel
bark (Plate 31, Fig. 2) the walls are thick, white, and very porous.
In some cells the branches are of equal length; in others they are
unequal. In the tea-leaf (Plate 31, Fig. 1) the walls are yellowish
white and finely porous. When the lower wall is brought in focus, it
shows numerous circular pits. These pits represent the pores viewed
from the end. The branches frequently branch or fork.
Branched stone cells also occur in coto bark, acer spicatum,
star-anise, witch-hazel leaf, hemlock, and wild-cherry barks.
Non-branched stone cells are divided into two main groups, as follows:
1. Porous and striated stone cells, and,
2. Porous and non-striated stone cells.
POROUS AND STRIATED STONE CELLS
=Porous and striated= walled stone cells occur in ruellia root,
winter’s bark, bitter root, allspice, and aconite. These stone cells
are shown in Plate 33, Figs. 1, 2, 3, 4, and 5.
The stone cells of ruellia root (Plate 32, Fig. 1) are greatly
elongated, rectangular in form, with thick, white, strongly porous
walls. The central cavity is narrow and is marked with prominent
pores and striations.
The stone cells of winter’s bark (Plate 32, Fig. 2) vary from
elongated to nearly isodiametric. The pores are very large, the light
yellowish wall is irregularly thickened, and the central cavity is
very large. The pores are prominent.
[Illustration: PLATE 31
BRANCHED STONE CELLS
1. Tea leaf (_Thea sinensis_, L.).
2. Witch-hazel bark (_Hamamelis virginiana_, L.).
3. Hemlock bark (_Tsuga canadensis_, [L.] Carr).
4. Wild-cherry bark (_Prunus serotina_, Ehrh.).]
The stone cell of bitter root (Plate 32, Fig. 3) is nearly
isodiametric. The walls are yellowish white and strongly porous and
striated. The central cavity is about equal to the thickness of the
walls.
The stone cell of allspice (Plate 32, Fig. 4) is mostly rounded in
form, and when the outer wall only is in focus it shows numerous
round and elongated pores. The central cavity is filled with masses
of reddish-brown tannin. The striations are very prominent.
The diagnostic stone cell of aconite (Plate 32, Fig. 5) is
rectangular or square in outline; the walls are yellowish and the
central cavity has a diameter many times the thickness of the
wall. The side and surface view of the pores is prominent, and the
striations are very fine.
POROUS AND NON-STRIATED STONE CELLS
=Porous and non-striated stone cells= occur in Ceylon cinnamon, in
calumba root, in dogwood bark, in cubeb, and in echinacea root.
The diagnostic stone cells of Ceylon cinnamon (Plate 33, Fig. 1) are
nearly square in outline; the walls are strongly porous and the large
central cavity frequently contains starch.
The stone cells of calumba root (Plate 33, Fig. 2) vary in shape from
rectangular to nearly square, and the walls are greenish yellow,
unequally thickened, and strongly porous. The typical stone cells
contain several prisms, usually four.
The stone cells of dogwood bark (Plate 33, Fig. 3) have thick, white
walls with simple and branched pores. The central cavity frequently
branches and appears black when recently mounted, owing to the
presence of air.
The stone cells of cubeb (Plate 33, Fig. 4) are very small, mostly
rounded in outline, with a great number of very fine simple pores
which extend from the outer wall to the central cavity. The wall is
yellow and very thick.
The stone cells of echinacea root (Plate 33, Fig. 5) are very
irregular in form; the walls are yellowish and porous, and the
central cavity is very large. A black intercellular substance is
usually adhering to portions of the outer wall.
The color of the walls of the different stone cells is very
variable. In Ceylon cinnamon and ruellia the walls are colorless;
in zanthoxylium, light yellow; in rumex, deep yellow; in cascara
sagrada, greenish yellow.
The pores of stone cells, like the pores of bast fibres, are either
simple or branched, and they may or may not extend through the entire
wall. Many of the shorter pores extend for only a short distance from
the cell cavity.
The width of the cell cavity varies considerably in the stone cells
of the different plants. In aconite (Plate 32, Fig. 5), in calumba
(Plate 33, Fig. 2), and in Ceylon cinnamon (Plate 33, Fig. 1), the
cell cavity is several times greater than the thickness of the cell
wall.
In allspice (Plate 32, Fig. 4), in bitter root (Plate 32, Fig. 3),
the diameter of the cell cavity and the thickness of the wall are
about equal. In cubeb (Plate 33, Fig. 4), in ruellia (Plate 32, Fig.
1), the wall is thicker than the diameter of the cell cavity.
The cavity of many stone cells contains no characteristic
cell contents. In other stone cells the cell contents are as
characteristic as the stone cell. The stone cells of both Saigon and
Ceylon cinnamon (Plate 33, Fig. 1) contain starch; the stone cells
of calumba (Plate 33, Fig. 2) contain prisms of calcium oxalate; the
stone cells of allspice and sweet-birch bark contain tannin.
In cross-sections, stone cells occur singly, as in Saigon cinnamon
(Plate 34, Fig. 1), ruellia (Plate 34, Fig. 2); in groups, as in
cascara sagrada (Plate 34, Fig. 3); and in continuous bands, as in
Saigon cinnamon (Plate 34, Fig. 4).
In powdered drugs, stone cells, like bast fibres, occur singly, as
in ruellia, calumba, etc.; or in groups, as in cascara sagrada,
witch-hazel bark, etc. In most powders they occur both singly and in
groups.
The individual stone cells are mostly entire, as in ruellia, calumba,
allspice, echinacea, etc. In cascara sagrada many of the stone cells
are broken when the closely cemented groups are torn apart in the
milling process. Many of the branched stone cells of witch-hazel bark
and leaf, wild cherry, etc., also occur broken in the powder.
[Illustration: PLATE 32
POROUS AND STRIATED STONE CELLS
1. Ruellia root (_Ruellia ciliosa_, Pursh.).
2. Winter’s-bark (_Drimys winteri_, Forst.).
3. Bitterroot (_Apocynum androsæmifolium_, L.).
4. Allspice (_Pimenta officinalis_, Lindl.).
5. Aconite (_Aconitum napellus_, L.).]
[Illustration: PLATE 33
POROUS AND NON-STRIATED STONE CELLS
1. Ceylon cinnamon (_cinnamomum zeylanicum_, Nees).
2. Calumba root (_Jateorhiza palmata_, [Lam.] Miers).
3. Dogwood root bark (_Cornus florida_, L.).
4. Cubeb (_Piper cubeba_, L., f.)
5. Echinacea (_Echinacea angustifolia_, D.C.).]
[Illustration: PLATE 34
1. Saigon cinnamon.
2. Ruellia root (_Ruellia ciliosa_, Pursh.).
3. Cascara sagrada (_Rhamnus purshiana_, D.C.).
4. Saigon cinnamon.]
The walls of all stone cells are composed of lignin.
The form of stone cells varies greatly; in aconite the stone cells
are quadrangular; in ruellia they are rectangular; in pimenta,
they are circular or oval in outline; in most stone cells they are
polygonal.
The lignified walls of stone cells are stained red with a solution of
phloroglucin and hydrochloric acid, and the walls are stained yellow
by aniline chloride.
ENDODERMAL CELLS
The =endodermal cells= of the different plants vary greatly in form,
color, structure, and composition of the wall, yet these different
endodermal cells may be divided into two groups: first, thin-walled
parenchyma-like cells, and secondly, thick-walled fibre-like cells.
In the thin-walled endodermal cells the walls are composed of
cellulose, and the cell terminations are blunt or rounded. When the
drug is powdered, the cells break up into small diagnostic fragments.
In the thick-walled endodermal cells, the walls are lignified and
porous, and the ends of the cell are frequently pointed and resemble
fibres.
Sarsaparilla root, triticum, convallaria, and aletris have
thick-walled endodermal cells.
STRUCTURE OF ENDODERMAL CELLS
The endodermal cells of sarsaparilla root (Plate 35, Fig. 1) are
never more than one layer in thickness. The walls are porous and of
a yellowish-brown color. Alternating with the thick-walled cell is a
thin-walled cell, which is frequently referred to as a passage cell.
The endodermal cells of triticum (Plate 35, Fig. 2) are yellowish,
and the walls are porous and striated. There are one or two layers
of cells. The cells forming the outer layer have very thin outer but
thick inner walls, while the cells forming the inner layer are more
uniform in thickness.
The endodermal cells of convallaria (Plate 35, Fig. 3) are yellowish
white in color, and the walls are porous and striated. The outer wall
of the layer of cells is thinner than the inner wall. The innermost
layer of cell is more uniformly thickened.
[Illustration: PLATE 35
CROSS-SECTIONS OF ENDODERMAL CELLS OF
1. Sarsaparilla root (_Smilax officinalis_, Kunth).
2. Triticum (_Agropyron repens_, L.).
3. Convallaria (_Convallaria majalis_, L.).
4. Aletris (_Aletris farinosa_, L.).]
The endodermal cells of aletris (Plate 35, Fig. 4) are yellowish
brown, slightly porous and striated. There are one or two layers of
these cells, and two of the smaller cells usually occupy a space
similar to that occupied by the radically elongated single cell.
On a longitudinal view, the endodermal cells of sarsaparilla
triticum, convallaria, and aletris appear as follows:
Those of sarsaparilla (Plate 36, Fig. 1) are greatly elongated, the
ends of the cells are blunt or slightly pointed, and the walls appear
porous and striated.
Those of triticum (Plate 36, Fig. 2) are elongated, the walls are
porous and striated, and the outer wall is much thinner than the
inner wall. The end wall between two cells frequently appears common
to the two cells.
Those of convallaria (Plate 36, Fig. 3) are elongated, and the end
wall is usually blunt. The outer wall is thinner than the inner wall.
Those of aletris (Plate 36, Fig. 4) are fibre-like in appearance; the
ends of the cells are pointed and the wall is strongly porous. The
longitudinal view of these cells is shown in plate 36.
HYPODERMAL CELLS
=Hypodermal cells= occur in sarsaparilla root and in triticum.
In the cross-section of sarsaparilla root (Plate 37, Fig. 1) the
hypodermal cells are yellowish or yellowish brown. The outer wall is
thicker than the inner wall, and the cell cavity is mostly rounded,
and contains air. The walls are porous and finely striated. On
longitudinal view, the hypodermal cells of sarsaparilla (Plate 37,
Fig. 2) are greatly elongated, and the outer and side walls are
thicker than the inner walls. The ends of the cells are blunt and
distinct from each other.
In cross-section, the hypodermal cells of triticum (Plate 37, Fig. 3)
are nearly rounded in outline, and the walls are of nearly uniform
thickness. In longitudinal view (Plate 37, Fig. 4) the same cells
appear parenchyma-like, and the walls between any two cells appear
common to the two cells.
[Illustration: PLATE 36
LONGITUDINAL SECTIONS OF ENDODERMAL CELLS
1. Sarsaparilla root (_Smilax officinalis_, Kunth).
2. Triticum (_Agropyron repens_, L.).
3. Convallaria (_Convallaria majalis_, L.).
4. Aletris (_Aletris farinosa_, L.).]
[Illustration: PLATE 37
HYPODERMAL CELLS
1. Cross-section sarsaparilla root (_Smilax officinalis_, Kunth).
2. Longitudinal section sarsaparilla root (_Smilax officinalis_,
Kunth).
3. Cross-section triticum (_Agropyron repens_, L.).
4. Longitudinal section triticum (_Agropyron repens_, L.).]
CHAPTER IV
ABSORPTION TISSUE
Most plants obtain the greater part of their food, first, from the
soil in the form of a watery solution, and, secondly, from the air
in the form of a diffusible gas. In a few cases all food material is
obtained from the air, as in the case of epiphytic plants. In such
plants, the aerial roots have a modified outer layer--velamen--which
functions as a water-absorbing and gas-condensing tissue. Many
xerophytic plants absorb water through the trichomes of the leaf.
Such absorption tissue enables the plant to absorb any moisture that
may condense upon the leaf and that would not otherwise be available
to the plant. The water-absorbing tissue of roots is restricted to
the root hairs, which are found, with few exceptions, only on young
developing roots.
ROOT HAIRS
=Root hairs= usually occur a short distance back of the root cap.
There is, in fact, a definite zone of the epidermis on which the root
hairs develop. This zone is progressive. As the root elongates the
root hairs continue to develop, the zone of hairs always remaining at
about the same distance from the root cap. With the development of
new zones of growth the hairs on the older zone die off and finally
become replaced by an epidermis, or a periderm, except in the case of
sarsaparilla root, and possibly other roots that have persistent root
hairs.
Each root hair is an outgrowth from an epidermal cell (Plate 38, Fig.
3). The length of the hair and its form depend upon the nature of the
soil, whether loose or compact, and upon the amount of water present.
A root hair is formed by the extension of the peripheral wall of
an epidermal cell. At first this wall is only slightly papillate,
but gradually the end wall is extended farther and farther from
the surface of the root, caused by the development of side walls by
the growing tip of the root hair until a tube-like structure, root
hair, is produced. The root hair is then a modified epidermal cell.
The protoplast lines the cell, and the central part of the root
hair consists of a large vacuole filled with cell sap. The wall of
the root hair is composed of cellulose, and the outermost part is
frequently mucilaginous. As the root hairs develop, they become bent,
twisted, and of unequal diameter, as a result of growing through
narrow, winding soil passages. During their growth, the root hairs
become firmly attached to the soil particles. The walls of root hairs
give an acid reaction caused by the solution of the carbon dioxide
excreted by the root hair. The acid character of the wall attracts
moisture, and in addition has a solvent action on the insoluble
compounds contained in the soil. It will thus be seen that the method
of growth, structure, composition, and reaction of the wall of the
root hair is perfectly suited to carry on the work of absorbing the
enormous quantities of water needed by the growing plant. It is
a well-known fact that when two solutions of unequal density are
separated by a permeable membrane, the less dense liquid will pass
through the membrane to the denser liquid. The wall of the root hair
acts like an osmotic membrane. The less dense watery solution outside
the root hair passes through its wall and into the denser cell sap
solution. As the solution is absorbed, it passes from the root hair
into the adjoining cortical parenchyma cells.
It is a fact that root hairs are seldom found in abundance on
medicinal roots. This is due to the fact that root hairs occur
only on the smaller branches of the root, and that when the root
is pulled from the ground the smaller roots with their root hairs
are broken off and left in the soil. For this reason a knowledge of
the structure of root hairs is of minor importance in the study of
powdered drugs. An occasional root hair is found, however, in most
powdered roots, but root hairs have little or no diagnostic value,
except in false unicorn root and sarsaparilla. When false unicorn
root is collected, most of the root hairs remain attached to the
numerous small fibrous roots, owing to the fact that these roots are
easily removed from the sandy soil in which the plants grow. The
root hairs of false unicorn are so abundant and so large that they
form dense mats, which are readily seen without magnification. These
hairs are, therefore, macroscopically as well as microscopically
diagnostic. The root hairs of false unicorn (Plate 39, Fig. 2) have
white, wavy, often decidedly indented walls. The terminal, or end
wall, is rounded and much thicker than the side walls.
[Illustration: PLATE 38
CROSS-SECTION OF SARSAPARILLA ROOT (_Smilax officinalis_, Kunth)
1. Epidermal cell developing into a root hair.
2. Developing root hair.
3. Nearly mature root hair.
4. Hypodermal cells.]
[Illustration: PLATE 39
ROOT HAIRS (Fragments)
1. Sarsaparilla root (_Smilax officinalis_, Kunth).
2. False unicorn root (_Helonias bullata_, L.).]
In sarsaparilla (Plate 39, Fig. 1) the root hairs are curved and
twisted. The end wall is thicker than the side walls. In some hairs
the walls are as thick as the walls of the thin-walled bast fibres.
This accounts for the fact that the root hairs are persistent on
even the older portions of sarsaparilla root, and it serves also to
explain why these root hairs remain on the root even after being
pulled from the firmly packed earth in which the root grows.
WATER ABSORPTION BY LEAVES
In many xerophytic terrestrial plants, the trichomes occurring on
leaves act as a water-absorbing tissue. In such plants the walls
of the hairs are composed largely of cellulose. It is obvious that
these hairs absorb the water of condensation caused by dew and light
rains--water which could not reach the plant except by such means.
There is no special tissue set aside for the absorption of gases from
the air. Carbon dioxide, which contributes the element carbon to the
starch formed by photosynthesis, enters the leaf by way of the stoma
and lenticels. The structure and the chief functions of these will be
considered under aërating tissue.
CHAPTER V
CONDUCTING TISSUE
All cells of which the primary or secondary function is that
of conduction are included under conducting tissue. It will be
understood how important the conducting tissue is when the enormous
quantity of water absorbed by a plant during a growing season is
considered. It will then be realized that the conducting system must
be highly developed in order to transport this water from one organ
to another, and, in fact, to all the cells of the plant. Special
attention must be given to the occurrence, the structure, the
direction of conduction, and to the nature of the conducted material.
The cells or cell groups comprising the conducting tissue are vessels
and tracheids, sieve tubes, medullary ray cells, latex tubes, and
parenchyma.
VESSELS
=Vessels= and =tracheids= form the principal upward conducting tissue
of plants. They receive the soil water expressed from the cortical
parenchyma cells located in the region of the root, immediately
back of the root hair zone. This soil water, with dissolved crude
inorganic and organic food materials, after entering the vessels
and tracheids passes up the stem. The cells needing water at the
different heights absorb it from the vessels, the excess finally
reaching the leaves. When the stem branches, the water passes into
the vessels of the branches and finally to the leaves of the branch.
In certain special cases the vessels conduct upward soluble food
material. In spring sugary sap flows upward through the vessels of
the sugar maple.
Vessels are tubes, often of great length, formed from a number of
superimposed cells, in which the end walls have become absorbed.
The vessels therefore offer little resistance to the transference
of water from the roots to the leaves of a plant. The combined
length of the vessels is about equal to the height of the plant in
which they occur. The length of the individual vessels varies from a
fraction of a meter up to several meters.
ANNULAR VESSELS
The =annular vessels= are thickened at intervals in the form of rings
(Plate 40, Fig. 1), which extend outward from and around the inner
wall of the vessel. In fact, it is the inner wall which is thickened
in all the different types of vessels. The ring-like thickening
usually separates from the wall when the drug is powdered. Such
separated rings occur frequently in powdered digitalis, belladonna,
and stramonium leaves. Annular vessels are not, however, of
diagnostic importance, because more characteristic cells are found in
the plants in which they occur. Not infrequently a vessel will have
annular thickenings at one end and spiral thickenings at the other.
Such vessels are found in the pumpkin stem (Plate 40, Fig. 1).
Vessels are distinguished from other cells by their arrangement, by
their large size when seen in cross-section, and by the thickening
of the wall when seen in longitudinal sections of the plant or in
powders. The side walls of vessels are thickened in a number of
striking yet uniform ways. The chief types of thickening of the wall,
beginning with one that is the least thickened, are annular, spiral,
sclariform, pitted, and pitted with bordered pores.
SPIRAL VESSELS
In the =spiral vessel= the thickening occurs in the form of a
spiral, which is readily separated from the side walls. This is
particularly the case in powdered drugs, where the spiral thickening
so frequently separates from the cell wall. There are three types of
spiral vessels: those with one (Plate 41, Fig. 1), those with two,
and those with three spirals. Single spirals occur in most leaves;
double spirals occur in many plants (Plate 41, Fig. 2), but they
are particularly striking in powdered squills. Triple spirals are
characteristic of the eucalyptus leaf (Plate 41, Fig. 3); in fact,
they form a diagnostic feature of the powder. Frequently a spirally
thickened wall indicates a developmental stage of the vessel. Many
such vessels are spirally thickened at first, but later, when
mature, an increased amount of thickening occurs and the vessel
becomes a reticulate or pitted vessel. Many mature vessels, however,
are spirally thickened as indicated above. In herbaceous stems and
in certain roots and leaves spiral vessels are associated with the
sclariform reticulate and pitted type. In certain cases a single
spiral band will branch as the vessel matures.
There is a great variation in the amount of spiral thickening
occurring in a vessel. In leaves, particularly, the spiral appears
loosely coiled; while in squills and other rhizomes and roots the
spiral appears as a series of rings. When viewed by high power only
half of each spiral band is visible. At either side of the cell the
exact size and form of the thickening appear in two parallel rows of
dark circles or projections from the walls. This thickening of the
wall is rendered visible from the fact that the light is retarded as
it passes through that portion of the spiral extending from the upper
to the under side of the spiral; while the light readily traverses
the upper and lower cross bands of the vessel.
It should be remembered that, when the upper part of the spiral
vessel is in focus, the bands appear to bend in a direction away from
the eye; while when the under side of the bands are in focus, the
bands appear to bend toward the eye. These facts will show that it
is necessary to focus on both the upper and lower walls in studying
spiral vessels. In double spiral vessels the spirals are frequently
coiled in opposite directions; therefore the bands appear to cross
one another. In eucalyptus leaf the three bands are coiled in the
same direction. In all cases the thickening occurs on all sides of
the wall. Its appearance will, therefore, be the same no matter at
what angle the vessel is viewed.
SCLARIFORM VESSELS
=Sclariform vessels= have interrupted bands of thickening on the
inner walls. Two or more such bands occur between the two side walls.
The series of bands are separated by uniformly thickened portions of
the wall extending parallel to the length of the vessel. Sclariform
vessels are usually quite broad, so that it is necessary to change
the focus several times in order to bring the different series of
bands in focus. The series of bands are usually of unequal width and
length.
[Illustration: PLATE 40
ANNULAR AND SPIRAL VESSELS
1. Pumpkin stem (_Cucurbita pepo_, L.).
2. Two characteristic views of spiral vessels.
3. (_A_) Upper part of spiral vessel in focus.
(_B_) Under part of spiral vessel in focus.
4. Spiral vessel of the disk petal matricaria (_Matricaria
chamomilla_, L.).]
[Illustration: PLATE 41
SPIRAL VESSELS
1. Single spiral vessel of pumpkin stem (_Cucurbita pepo_, L.).
2. Double spiral vessel of squill bulb (_Urginea maritima_, [L.]
Baker).
3. Triple spiral vessel of eucalyptus leaf (_Eucalyptus globulus_,
Labill).]
Sclariform vessels occur in male fern (Plate 42, Fig. 2), calamus,
tonga root (Plate 42, Fig. 3), and sarsaparilla (Plate 42, Fig. 1).
In each they are characteristic. Sclariform vessels, with these few
exceptions, do not occur in drug plants. In fact, drugs derived from
dicotyledones rarely have sclariform vessels. They occur chiefly
in the ferns and drugs derived from monocotyledenous plants. Their
presence or absence should, therefore, be noted when studying
powdered drugs.
RETICULATE VESSELS
=Reticulate vessels= are of common occurrence in medicinal plants. In
fact, they occur more frequently than any other type of vessel. The
basic structure of reticulate vessels (Plate 43, Fig. 1) occurring in
different plants is similar, but they vary in a recognizable way in
different plants (Plate 43, Fig. 2). The walls of reticulate vessels
are thickened to a greater extent than are the walls of spirally
thickened vessels.
PITTED VESSELS
=Pitted vessels= are met with most frequently in woods and
wood-stemmed herbs. There are two distinct types of pitted
vessels--_i.e._, simple pitted vessels and pitted vessels with
bordered pores.
The pitted vessel represents the highest type of cell-wall
thickening. The entire wall of the vessel is thickened, with the
exception of the places where the pits occur. The number and size of
the pits vary greatly in different drugs. In quassia (Plate 44, Fig.
1) the pits are numerous and very small, and the openings are nearly
circular in outline. In white sandalwood (Plate 44, Fig. 3). the pits
are few in number, but when they do occur they are much larger than
are the pits of quassia.
PITTED VESSELS WITH BORDERED PORES
=Pitted vessels with bordered pores= are of common occurrence in the
woody stems and stems of many herbaceous plants (Plate 45, Figs. 3
and 4). In such vessels the wall is unthickened for a short distance
around the pits. This unthickened portion may be either circular or
angled in outline, a given form being constant to the plant in which
it occurs. The pits vary from oval to circular. Pitted vessels with
bordered pores occur in belladonna and aconite stems.
[Illustration: PLATE 42
SCLARIFORM VESSELS
1. Sarsaparilla root (_Smilax officinalis_, Kunth).
2. Male fern (_Dryopteris marginalis_, [L.] A. Gray).
3. Tonga root.]
[Illustration: PLATE 43
RETICULATE VESSELS
1. Hydrastis rhizome (_Hydrastis canadensis_, L.).
2. Musk root (_Ferula sumbul_, [Kauffm.] Hook., f.).]
[Illustration: PLATE 44
PITTED VESSELS
1. Quassia, low magnification (_Picræna excelsa_, [Swartz] Lindl.).
2. Quassia, high magnification.
3. White sandalwood (_Santalum album_, L.).]
[Illustration: PLATE 45
VESSELS
1. Reticulate vessel of calumba root (_Jateorhiza palmata_, [Lam.]
Miers).
2. Reticulate tracheid of hydrastis rhizome (_Hydrastis
canadensis_, L.).
3. Pitted vessel with bordered pores of belladonna stem.
4. Pitted vessel with bordered pores of aconite stem (_Aconitum
napellus_, L.).]
Vessels and tracheids lose their living-cell contents when fully
developed. In the vessels the cell contents disappear at the period
of dissolution of the cell wall.
The walls of vessels and tracheids are composed of lignin, a
substance which prevents the collapsing of the walls when the
surrounding cells press upon them, and which also prevents the
tearing apart of the wall when the vessel is filled with ascending
liquids under great pressure. Lignin thus enables the vessel to
resist successively compression and tearing forces.
Tracheids are formed from superimposed cells with oblique perforated
end walls. The side walls of tracheids are thickened in a manner
similar to those of vessels. The tracheids in golden seal are of a
bright-yellow color, and groups of these short tracheids scattered
throughout the field form the most characteristic part of the
powdered drug. In ipecac root the tracheids are of a porcelain-white,
translucent appearance, and they are much longer than are the
tracheids of golden seal.
The cellulose walls of parenchyma cells are stained blue with
hæmatoxylin and by chlorzinciodide. Cellulose is completely soluble
in a fresh copper ammonia solution.
SIEVE TUBES
=Sieve tubes= are downward-conducting cells. They conduct downward
proteid food material. This fact is easily demonstrated by adding
iodine to a section containing sieve tubes, in which case the sieve
tubes are turned yellow.
Developing sieve tubes have all the parts common to a living cell;
but when fully mature, however, the nucleus becomes disorganized, but
a layer of protoplasm continues to line the cell wall.
Sieve tubes (Plate 46, Fig. 1) are composed of a great number of
superimposed cells with perforated end walls and with non-porous
cellulose side walls. The end walls of two adjoining cells are
greatly thickened and the pores pass through both walls. This
thickened part of the porous end walls of two sieve cells is called
the sieve plate, and it may be placed in an oblique or a horizontal
position.
[Illustration: PLATE 46
1. Longitudinal section of sieve tube (_Cucurbita pepo_, L.).
2. Cross-section of sieve tube just above an end wall--sieve plate.]
In a longitudinal section the sieve tubes are seen to be slightly
bulging at the sieve plate, and through the pores extend protoplasmic
strands. The strands are united on the upper and lower side of
the sieve plate to form the protoplasmic strands of the living
sieve tubes and the callus, layers of dried plants. This callus is
frequently yellowish in color, and in all cases is separated from the
cell wall. In certain plants the sieve plate occurs on the side walls
of the sieve tubes in contact with other sieve tubes.
SIEVE PLATE
=Sieve plates= on cross-section (Plate 46, Fig. 2) are polygonal
in outline, and the pores are either round or angled. Large sieve
tubes and sieve plates occur in pumpkin stem; but, almost without
exception, in drug plants the sieve tubes are small and the sieve
plate is inconspicuous. When the drug is powdered, the sieve tubes
break up into undiagnostic fragments. When studying sections of the
plants, the extent, size, and arrangement of the sieve tubes must
always be noted.
MEDULLARY BUNDLES, RAYS, AND CELLS
Function
The medullary ray cells are the lateral conducting cells of the
plant. They conduct outwardly the water and inorganic salts brought
up from the roots by the vessels and tracheids; and they conduct
inwardly toward the centre of the stem the food material manufactured
in the leaves and brought down by the sieve cells. The medullary rays
thus distribute the inorganic and organic food to the living cells of
the plant, and they conduct the reserve food material to the storage
cells, and, lastly, they function in certain plants as storage cells.
Occurrence
The form, size, wall structure, and the distribution of the medullary
ray bundles, rays, and cells are best ascertained by studying:
first, the cross-section of the plant; secondly, the radial section;
and, thirdly, the tangential section.
Students should be careful to distinguish between the medullary ray
bundle, the medullary ray, and the medullary ray cell. In some plants
the bundles are only one cell wide, but in other plants the medullary
ray bundle is more than one cell wide, frequently several cells wide.
THE MEDULLARY RAY BUNDLE
The =medullary ray bundle= is made up of a great many medullary ray
cells. These bundles (Plate 106, Fig. 5) are of variable length,
height, and width. The bundles are isolated, and they occur among
and separate the other cells of the plants in which they occur.
Tangential sections show the medullary ray bundle in cross-section.
Such sections are lens-shaped, and they show both the width and the
height of the medullary ray bundle. The length of the medullary ray
bundle is shown in cross-sections.
THE MEDULLARY RAY
The =medullary ray= (Plate 47) is a term used to indicate that part
of a medullary ray bundle which is seen in cross-sections and in
radial sections. In cross-sections the length of the ray will be as
great as the length of the bundle, and the width of the ray will be
as great as the width of the medullary ray bundle at the point cut
across. In longitudinal sections the medullary ray will differ in
height according to the thickness of the bundle at the point cut.
When the medullary rays extend from the centre of the stem to the
middle bark, they are termed primary medullary rays; when they extend
from the cambium circle to the middle bark, they are termed secondary
medullary rays. As the plant grows, the diameter of the organ becomes
greater and the number of medullary rays are increased. In each of
these cases the medullary rays may be one or more than one cell wide,
according to whether the medullary ray bundle is one or more than one
cell wide. Even in the same plant the width of the medullary rays
will vary if the bundle is more than one cell wide, according to
width of the medullary ray bundle at the point cut across.
[Illustration: PLATE 47
RADIAL LONGITUDINAL SECTION OF WHITE SANDALWOOD
(_Santalum album_, L.)
1. Medullary ray.
2. Wood fibres and wood parenchyma.]
On cross-section the medullary rays are seen to vary greatly. In many
plants they are more or less straight radial lines, as in quassia
(Plate 105, Fig. 2); while in other plants they form wavy lines
where they bend or curve around the conducting cells, as in piper
methysticum, kava-kava (Plate 48, Fig. A).
In the study of powdered drugs the radial view of the medullary rays
is most frequently seen.
In a perfect radial section (Plate 107, Fig. 2) the medullary rays
are seen as tiers of cells in contact throughout their long diameter,
and they run at right angles to the long diameter of the other cells.
This view of the rays shows the length and height of the medullary
ray. In logwood the rays are often forty cells high. In powdered
barks, woods (Plate 47), and woody roots the radial view of the
medullary rays is frequently diagnostic.
In guaiacum officianale wood the medullary rays are one cell wide on
cross-section, and up to six cells high on the tangential section.
In santalum album the rays are from one to three cells wide on
cross-section, and up to six cells high on tangential section. In the
greater number of plants the rays are more than one cell wide.
THE MEDULLARY RAY CELL
The =medullary ray cell= (Plate 48, Fig. 1) is one of the individual
cells making up the medullary ray bundle and the medullary ray.
The cross-sections of the cells which are seen in tangential sections
show the cells to be mostly circular in outline when they occur in
the central portion of medullary ray bundles of more than two cells
in width; but they are more irregular in outline when the medullary
ray bundle is only one cell wide. Even the cells of the three or more
cell-wide bundles have irregular, outlined cells at the ends of the
bundle and on the sides in contact with the other tissues.
The length and height of the medullary ray cell are shown in radial
sections; while the width and length of the medullary ray cells are
shown in cross-sections.
Structure of Cells
The structure of the individual cells forming the medullary rays
differs greatly in different plants, but is more or less constant in
structure in a given species.
The medullary rays of the wood usually have strongly pitted side and
end walls, while the medullary rays of most barks are not at all, or
only slightly, pitted. In most plants the cells are of nearly uniform
size. Frequently, however, the cells vary in size in a given ray, as
shown in the cross-section of kava-kava.
Arrangement of the Cells in a Ray
The union of any two cells in a ray is also of importance. In
quassia the medullary ray cells have oblique end walls, so that on
cross-section the line of union between two cells is an oblique
wall. In most plants the medullary ray cells have blunt or square or
oblique end walls, so that the line of union is a straight line.
In most plants the cells are much longer than broad, but the cells of
sassafras bark are nearly as broad as long.
The walls of the cortical medullary ray cells and the medullary rays
of most roots and stems of herbs are composed of cellulose; while
the walls of medullary ray cells occurring in woods are frequently
lignified.
There is a great variation in the character of the cell contents of
medullary rays. In white pine bark (Plate 48, Fig. B1) are deposits
of tannin; in quassia wood, starch; in canella alba, rosette crystals
of calcium oxalate, etc.
LATEX TUBES
Living =latex tubes=, like sieve tubes, have a layer of protoplasm
lining the walls, and, in addition, have numerous nuclei. In drug
plants the nuclei are not distinguishable, but the protoplasm is
always clearly discernible.
[Illustration: PLATE 48
_A._ Cross-section of kava-kava root (_Piper methysticum_,
Forst., f.).
1. Unequal diameter medullary ray cells.
2. Vessels.
3. Wood parenchyma.
4. Wood fibres.
_B._ Cross-section of white pine bark (_Pinus strobus_, L.).
1. Wavy medullary rays with tannin.
2. Parenchyma cells.
3. Sieve cells.]
Latex tubes function both as storage and as conducting cells. They,
like the sieve tubes, contain proteid substances chiefly, yet
frequently starch is found. The cells bordering the latex tubes
absorb from them, as needed, the soluble food material. While our
knowledge concerning the function of latex in some plants is meagre,
still in other plants it is practically certain that the latex is
composed of nutritive substances which are utilized by the plant as
food. In certain other plants the latex appears to be used as a means
of resisting insect attacks and as a protection against injury.
There are two types of latex tubes common to plants, namely, latex
cells and latex vessels. Latex tubes developing from a single cell do
not differ materially from a latex tube originating from the fusion
of several cells. In each case the latex tube branches to such an
extent that it bears no resemblance to ordinary cells. It would seem
that the ultimate branches are formed and develop in much the same
manner as root hairs--that is, by a growing tip of the branch. A
mature plant may therefore have latex tubes with almost numberless
branches (Plate 50, Fig. 1) and be of very great length.
The branches of latex tubes develop in such an irregular manner that
it is possible to obtain a cross and a longitudinal section of the
latex tubes by making a cross-section of stem. Such a section is
shown in the drawing of the cross-section of the rhizome of black
Indian hemp (Plate 49, Fig. B).
The color of the latex in medicinal plants varies from a gray white
in papaw (carica papaya), aromatic sumac, black Indian hemp, and
bitter root, to white in the opium poppy, light orange in celandine,
and deep orange in bloodroot (Plate 50, Fig. 2). In each of these
cases it is the latex which yields the important medicinal products.
PARENCHYMA
The larger amount of plant tissue is composed of =parenchyma= cells.
These cells vary from square to oblong, or they may be irregular and
branched. The end walls are square or blunt, and the wall is composed
of cellulose, with the exception of the wood parenchyma, which has
lignified walls.
There are seven characteristic types of parenchyma cells: (1)
cortical parenchyma, (2) pith parenchyma, (3) wood parenchyma,
(4) leaf parenchyma, (5) aquatic plant parenchyma, (6) endosperm
parenchyma, (7) phloem parenchyma.
[Illustration: PLATE 49
_A._ Cross-section of black Indian hemp (_Apocynum cannabinum_, L.).
1. Longitudinal section of a latex tube.
2. Cross-section of latex tube.
3. Parenchyma.
_B._ Cross-section of a part of black Indian hemp root.
4. Cross-section of a large latex tube.
5. Parenchyma.]
[Illustration: PLATE 50
LATEX VESSELS
1. Radial-longitudinal section of dandelion root (_Taraxacum
officinale_, Weber).
2. Cross-section of sanguinaria root (_Sanguinaria canadensis_, L.).
3. Cross-section of dandelion root.]
Parenchyma cells, cortical, pith, aquatic plant, leaf, flower,
and endosperm, conduct in all directions--upward, downward, and
laterally. The direction of conduction depends upon the needs of the
different cells forming the plant. The fluids pass from the cell with
an abundance of cell sap to the cell with less cell sap. In this wall
all cells are provided with food.
Parenchyma cells conduct water absorbed by the roots and soluble
carbohydrate material chiefly.
The walls of all the different types of parenchyma cells are composed
of cellulose with the exception of the wood parenchyma cells,
the walls of which are lignified. The end walls of non-branched
parenchyma cells and the cell terminations of branched cells are very
blunt.
CORTICAL PARENCHYMA
=Cortical parenchyma= (Plate 51) differs greatly in size, thickness
of the walls, and arrangement. A study of the longitudinal sections
of different parts of medicinal plants reveals the fact that the
cortical parenchyma cells form superimposed layers in which the end
walls are either parallel, in which case the arrangement resembles
that of several rows of boxes standing on end, or the end walls of
the cells alternate with each other, in which case the arrangement is
similar to that of the arrangement of the bricks in a building.
In certain plants the cortical parenchyma cells are long and narrow
and rectangular in shape, while in other plants the cells, although
still rectangular in outline, are very broad and approach the square
form.
All typical cortical parenchyma cells have uniformly thickened
non-pitted walls. In most barks the parenchyma cells beneath the
bark are elongated tangentially, but are very narrow radially. The
cells are always arranged around intercellular spaces, which vary
from triangular, quadrangular, etc., according to the number of cells
bordering the intercellular space.
PITH PARENCHYMA
=Pith parenchyma= (Plate 52) differs from cortical parenchyma cells
chiefly in the character of the walls, which are usually thicker and
always pitted.
[Illustration: PLATE 51
PARENCHYMA CELLS
1. Longitudinal section of the cortical parenchyma of celandine
root (_Chelidonium majus_, L.) 2. Cross-section of the cortical
parenchyma of sarsaparilla root (_Smilax officinalis_, Kunth).]
[Illustration: PLATE 52
_A._ Longitudinal section of the pith parenchyma of grindelia stem
(_Grindelia squarrosa_, [Pursh] Dunal).
1. Cell cavity.
2. Cross-section of the porous end wall.
3. Surface view of the porous side wall.
_B._ Cross-section of the pith parenchyma of grindelia stem.
1. Cell cavity.
2. Porous walls.
3. Pitted end walls.]
LEAF PARENCHYMA
The =parenchyma cells= (Plate 109, Fig. 1) of leaves, of flower
petals, and the parenchyma cells of some aquatic plants are branched;
that is, each cell has more than two cell terminations. These cell
terminations are frequently quite attenuated and usually very blunt.
Such a cell structure provides for a greater amount of intercellular
space and a maximum exposure of surface. This arrangement makes it
possible for the parenchyma cells of the leaf to absorb more readily
the enormous amount of carbon dioxide needed in the photosynthetic
process.
AQUATIC PLANT PARENCHYMA
The =parenchyma of aquatic plants= (Plate 59) has large intercellular
spaces formed by the chains of cells.
WOOD PARENCHYMA
=Wood parenchyma= (Plate 105, Fig. 3) cells are the narrowest
parenchyma cells occurring in the plant. Their walls are always
lignified and strongly pitted, and in some cases the end walls common
to two cells are obliquely placed.
PHLOEM PARENCHYMA
=Phloem parenchyma= (Plate 100, Fig. 8) cells are usually associated
with sieve cells. They are very long, narrow, and have thin,
non-pitted walls. The thinness of the walls undoubtedly enables the
cells to conduct diffusible food substance more quickly than the
cortical parenchyma cells.
PALISADE PARENCHYMA
=Palisade parenchyma= of leaves is of the typical parenchyma shape
and the end walls are placed nearly on a plane, even when more than
one layer is present. The cells are very small, however, and the
walls are very thin and non-pitted.
CHAPTER VI
AERATING TISSUE
The =aerating tissue= of the plant performs a threefold function:
first, it permits the exchange of gases during photosynthesis;
secondly, it permits the entrance of oxygen and the exit of carbon
dioxide during respiration; and, thirdly, it permits the exit of the
excess of water absorbed by the plant.
The above functions are carried on by the stomata, the water-pores,
the lenticels, and the intercellular spaces of the plant. The stoma
functions as the chief channel for the passage of CO₂-laden air into
the leaf and of oxygen-laden air from the leaf to the atmosphere. The
stoma also functions as an organ of transpiration, since through the
stoma a large part of the excess water of the plant passes off into
the air.
WATER-PORES
In certain plants the primary epidermis is provided with openings
resembling stomata, but unlike stomata the orifice remains open, and
instead of being located on the upper or lower surface of the leaf,
they are located on the margin of leaves immediately outward from the
veins. Water is given off to the atmosphere from these openings. Such
an opening is usually designated as a water-pore.
STOMATA
The chief external openings of the epidermis of leaves, of herbs, and
of young wood stems are known as stomata. Surrounding the stoma are
two cells known as guard cells.
=Guard cells= differ greatly in form, in size, in arrangement, in
occurrence, in association, in abundance (Plates 53, 54, and 55), and
in color. The guard cells surrounding the stoma vary in form from
circular to lens-shaped. In most leaves the outline of the guard
cells is rounded or has a curved outline; but in a few cases the
guard cells have angled outlines.
[Illustration: PLATE 53
1. Stoma and surrounding cells of aconite stem (_Aconitum
napellus_, L.).
2. Stoma and angled striated walled surrounding cells of peppermint
stem (_Mentha piperita_, L.). 3. Stoma and elongated surrounding
cells of lobelia stem (_Lobelia inflata_, L.).]
[Illustration: PLATE 54
TYPES OF STOMA
1. Under epidermis of short buchu (_Barosma betulina_, [Berg.]
Bartling and Wendl., f.) showing stoma and deposits of hesperidin.
2. Under epidermis of Alexandria senna (_Cassia acutifolia_,
Delile) showing stoma and thick-angled walled surrounding cells.
3. Upper epidermis of eucalyptus leaf (_Eucalyptus globulus_,
Labill.) showing sunken stoma and slightly beaded walled
surrounding cells.
4. Under epidermis of belladonna leaf (_Atropa belladonna_, L.)
showing stoma and wavy, striated, walled epidermal cells.]
The =arrangement of the surrounding cells= of the stoma is one of the
most important characteristics of the different leaves. As a rule the
number of surrounding cells about a stoma is constant for a given
species. In senna leaves (Plate 54, Fig. 2) there are normally two
surrounding cells about each guard cell, while in coca there are four
(Plate 55, Fig. 1). In senna the long diameter of the surrounding
cells is parallel to the long diameter of the guard cells; but in
coca the long diameter of two surrounding cells is at right angles to
the long diameter of the guard cells, while two cells are parallel to
the long diameter of the guard cells.
In most leaves there are more than two cells around the guard cells.
The form and size of the surrounding cells must always be considered.
In most leaves they are variable in size and form.
Guard cells occur first, even with the surface of the leaf (Plate 56,
Fig. A); secondly, above the surface of the leaf (Plate 56, Fig. B);
and, thirdly, below the surface of the leaf. (Plate 56, Fig. C). Only
one of the above types occurs in a given species of plant. That is,
plants with stomata above the surface of the leaf do not have stomata
on a level with or below the leaf surface.
The number of stomata on a given surface of a different leaf varies
considerably.
In many of the medicinal leaves stomata occur only on the under
surface of the leaf. In other leaves stomata occur on both surfaces
of the leaf; but in such cases there are a greater number on the
under surface.
In certain leaves the long diameter of the guard cells is parallel to
the length of the leaf; in other cases the long diameter of the stoma
is arranged at right angles to the length of the leaf.
In other leaves the arrangement is still more irregular, the guard
cells assuming all sorts of positions in relation to the length of
the leaf.
[Illustration: PLATE 55
LEAF EPIDERMI WITH STOMA
1. Under epidermis of coca leaf (_Erythroxylon coca_, Lam.) with
stoma on a level with the surface.
2. Under epidermis of false buchu (_Marrubium peregrinum_, L.) with
stoma below the level of the surface.
3. Upper epidermis of deer tongue (_Trilisa odoratissima_, [Walt.]
Cass.) with stoma above the leaf surface.]
[Illustration: PLATE 56
_A._ Cross-section of belladonna leaf (_Atropa belladonna_, L.).
1, Epidermal cells; 2, Guard cells even with the leaf surface; 3,
Surrounding cells; 4, Air space below the guard cells; 5, Palisade
cells; 6, Mesophyll cells. _B._ Cross-section of deer tongue leaf,
1. Epidermal cells; 2, Guard cells above the surface of the leaf;
3, Surrounding cells; 4, Air space below the guard cells; 5,
Hypodermal cells. _C._ Cross-section of white pine leaf (_Pinus
strobus_, L.). 1, Epidermal and hypodermal cells; 2, Guard cells
below the leaf surface; 3, Surrounding cells; 4, Air space below
the guard cells; 5, Parenchyma cells with projecting inner walls.]
The =relation of the stoma to surrounding cells= is best shown in
cross-sections of the leaf. In powders the relationship of the stoma
to the surrounding cells is, however, readily ascertained. If the
guard cells come in focus first, they are above the surface; if the
guard cells and the surrounding cells come in focus at the same time,
the stomata are even with the surface; if the stomata come in focus
after the surrounding cells, they are below the surface of the leaf.
The relationship of the stoma to the surrounding cells should always
be ascertained, not only in cross-sections of the leaf, but also in
powders.
There is the greatest possible variation in the size of guard cells.
This fact must always be kept in mind when studying leaves. This
variation in the size of the guard cells is clearly illustrated by
coca, senna, and by deer’s-tongue. In coca the stomata are very
small; in senna they are larger; while in deer’s-tongue the stomata
are very large.
The width and length of the stoma or opening between the guard cells
are of a character which must not be overlooked. Generally speaking,
those leaves which have large guard cells will have correspondingly
large stomata.
The guard cells usually contain chloroplasts showing various stages
of decomposition.
In bay-rum leaf the guard cells are of a bright reddish-brown color,
but in most leaves the guard cells are colorless.
LENTICELS
=Lenticels= are small openings occurring in the bark of plants.
The lenticels bear the same relationship to the stem that the
stomata do to the leaves. Lenticels, like stomata, have a threefold
function--namely, exchange of gases in photosynthesis, in
respiration, and the giving off of water.
Lenticels are macroscopically as well as microscopically important.
When unmagnified the lenticels are circular, lens-shaped, or
irregular in outline. They are arranged in parallel longitudinal
lines or parallel transverse lines, or they are irregularly
scattered. The latter is the usual arrangement. In most cases they
are elevated slightly above the surface of the bark. In root barks
particularly the lenticels stand out prominently from the surface of
the bark and in many cases appear stalked.
The color of the lenticels differs greatly in the different plants.
In acer spicatium they are brown; in witch-hazel they are gray; in
xanthoxylium they are yellowish; and lastly, the number of lenticels
occurring in a given surface of the bark should always be considered.
On cross-sections the lenticel (Plate 57, Fig. 2) is seen to have
a central depressed portion made up of loosely arranged cells.
Bordering the cavity are typical cork cells. The cork cells
immediately surrounding the lenticels are usually darker in color,
and many of the cells are partly broken down.
The size of lenticels will vary according to the type of the
lenticel. In studying sections more attention should be paid to the
character of the cells forming the lenticels than to the size of the
lenticel.
On cross-section the intercellular spaces (Plate 58) are triangular,
quadrangular, or irregular. The spaces between equal diameter
parenchyma cells is triangular if three cells surround the space, and
quadrangular if four cells surround the space, etc. These spaces are
in direct contact with similar spaces that traverse the tissue at
right angles to its long axis.
The branched mesophyll cells of the leaf and aquatic plant parenchyma
(Plate 59) are arranged around irregular cavities. In leaves and
aquatic plants these spaces run parallel to the long axis of the
organ.
In each of the above cases the cavity is formed by the separation of
the cell walls. There is still another type of irregular cavities
which is formed by the dissolution or tearing apart of the cell
walls. Such cavities are found in the stems and roots of many herbs.
The pith cells in the stems of many herbs become torn apart during
the growth of the stem, with the result that large irregular cavities
are formed. These cavities are usually filled with circulatory air.
In the stems of conium, cicuta, angelica, and other larger herbaceous
stems the pith separates into layers. When a longitudinal section
is made of such a stem it is seen to be composed of alternating air
spaces and masses of pith parenchyma.
The intercellular spaces are very large in leaves where enormous
quantities of carbon dioxide are vitalized in photosynthesis.
[Illustration: PLATE 57
CROSS-SECTION OF ELDER BARK (_Sambucus canadensis_, L.). 1.
Periderm. 2. Lenticel. 3. Phellogen.]
[Illustration: PLATE 58
INTERCELLULAR AIR SPACES
_A._ Cross-section of uva-ursi leaf (_Arctostaphylos uva-ursi_,
[L.] Spreng.).
1. Irregular intercellular air spaces.
_B._ Cross-section of the cortical parenchyma of sarsaparilla
root (_Smilax officinalis_, Kunth). 1, Triangular intercellular
spaces; 2, Quadrangular intercellular air spaces; 3, Pentagular
intercellular air spaces.]
[Illustration: PLATE 59
IRREGULAR INTERCELLULAR AIR SPACES
1. Skunk-cabbage (_Symplocarpus fœtidus_, [L.] Nutt.)
2. Calamus rhizome (_Acorus calamus_, L.).]
In the rhizome of calamus and other aquatic plants the intercellular
spaces are very large. The cells of these plants are arranged in
the form of branching chains of cells which thus provide for large
intercellular spaces.
The cells of the middle layer of flower petals, like the mesophyll of
leaves, is loosely arranged owing to the peculiar branching form of
the cells.
Seeds and fruits contain, as a rule, few or no intercellular spaces.
CHAPTER VII
SYNTHETIC TISSUE
Under synthetic tissue are grouped all tissues and cells which form
substances or compounds other than protoplasm. Such compounds are
stored either in special cavities or in the cells of the plant, as
the glandular hairs; internal secreting cavities of barks, stems,
leaves, fruits, seeds, and flowers; photosynthetic cells or cells
with chlorophyll, and the parenchymatic cells which form starch,
sugar, fats, alkaloids, etc.
PHOTOSYNTHETIC TISSUE
The most important non-glandular synthetic tissue is the
photosynthetic tissue, which is composed of the chlorophyll-bearing
cells of the plant. These are the so-called green cells of leaves, of
stems of herbs, of young woody stems, and in the older woody stems of
plants like wild cherry, birch, etc. The greater part of the tissue
of leaves is composed of chlorophyll-bearing cells.
Leaves collectively constitute the greatest synthetic manufacturing
plant in the world, because the green cells of the leaf produce most
of the food of men and animals. The two compounds utilized in the
manufacture of food are carbon dioxide (CO₂) and water (H₂O). These
two compounds are combined by chlorophyll through the agency of light
into starch. Chemically this reaction may be expressed as follows:
6CO₂ + 5H₂O = 2C₆H₁₀O₅ + 6O₂.
During the day a large quantity of starch is formed. At night through
the action of a ferment the excess of starch remaining in the leaf
is converted into sugar (C₆H₁₂O₆) - C₆H₁₀O₅ + H₂O = C₆H₁₂O₆. In this
form it is distributed to the living cells of the plant. The presence
or absence of starch in leaves is easily ascertained by placing the
leaf in hot alcohol to remove the chlorophyll, and by adding Lugol’s
solution. If starch is present, the contents of the cells will become
bluish black; but if no starch is present, the cells remain colorless.
GLANDULAR TISSUE
The =glandular tissue= of the plant is divided into two groups,
according to where it occurs. These groups are, first, =external=
glandular tissue, and secondly, =internal= glandular tissue. The most
important external glandular tissue is composed of the glandular
hairs. These are divided into two groups: first, =unicellular=; and
secondly, =multicellular= glandular hairs.
UNICELLULAR GLANDULAR HAIRS
The =unicellular glandular hairs= are either sessile or stalked.
=Sessile unicellular hairs= occur in digitalis leaves.
=Stalked unicellular hairs= of digitalis are shown on Plate 60, Fig.
2.
=Unicellular uniseriate stalked glandular hairs= occur on the stems
of the common house geranium (Plate 61, Fig. 2), on the leaves of
butternut, the leaves and stems of marrubium peregrinum (Plate 98,
Fig. 5), and in arnica flowers. The stalk varies from two to ten
cells; in eriodictyon the cells vary from four to eight cells.
Unicellular multiseriate stalked glandular hairs are not of common
occurrence.
MULTICELLULAR GLANDULAR HAIRS
=Multicellular glandular hairs= are divided into two groups: first,
sessile; and secondly, stalked hairs.
Multicellular sessile glandular hairs occur on the leaves of
peppermint (Plate 60, Fig. 3), horehound (Plate 97, Fig. 7), and
in hops (Plate 60, Fig. 4). In each of these hairs there are eight
secretion cells.
=Stalked glandular hairs= are divided into two groups: first,
uniseriate stalked; and secondly, multiseriate stalked glandular
hairs.
=Multicellular uniseriate stalked glandular hairs= occur on the
leaves of tobacco (Plate 61, Fig. 4), belladonna (Plate 61, Fig. 1),
and digitalis (Plate 60, Fig. 2), and of the fruit of rhus glabra.
[Illustration: PLATE 60
GLANDULAR HAIRS
1. Kamala (_Mallotus philippinensis_, [Lam.] [Muell.] Arg.).
2. Digitalis leaf (_Digitalis purpurea_, L.).
3. Peppermint leaf (_Mentha piperita_, L.).
4. Lupulin.
5. Cannabis indica leaf (_Cannabis saliva_, L.).]
=Multicellular multiseriate stalked glandular hairs= occur on the
stems and leaves of cannabis indica (Plate 60, Fig. 5).
In the glandular hair of kamala (Plate 60, Fig. 1) the number of
secretion cells is variable and papillate in form, and the cuticle is
separated from the secretion cells.
In the glandular hair of hops the outer wall or cuticle is torn away
from the secretion cells, and the cavity thus formed serves as a
storage cavity. This distended cuticle of the hops shows the outline
of the cells from which it was separated.
In the glandular hairs of the mints the secreted products (volatile
oils) are stored between the secretion cells and the outer detached
cuticle. This cuticle is elastic, and it becomes greatly distended as
the volatile oil increases in amount.
In many of the so-called glandular hairs, tobacco, belladonna
geranium, etc., the synthetic products are retained in the glandular
cells, there being no special cavity for their storage.
These hairs usually contain an abundance of chlorophyll.
The division wall of multicellular glandular hairs may be vertical,
as in the two-celled hair of digitalis (Plate 60, Fig. 2); as in
horehound (Plate 97, Fig. 6), and as in peppermint (Plate 60, Fig.
3); in this case there are eight cells, and they form a more or less
flat plate of cells.
In other hairs the division wall is horizontal; this produces a chain
of superimposed secreting cells, as in some of the glandular hairs of
belladonna leaf (Plate 61, Fig. 1), etc.
In other hairs the division walls are both vertical and horizontal,
as in tobacco (Plate 61, Fig. 4), henbane (Plate 61, Fig. 3),
belladonna (Plate 61, Fig. 1).
Other characters to be kept in mind in studying glandular hairs are
the following: Color of cell contents; size of the cells, whether
uniform or variable; character of wall, whether smooth or rough.
SECRETION CAVITIES
=Secretion cavities= are divided into three groups, according to the
nature of the origin of the cavity: first, schizogenous cavities,
which originate by a separation of the walls of the secretion cells;
secondly, lysigenous cavities, which arise by the dissolution
of the walls of centrally located secretion cells; and thirdly,
schizo-lysigenous cavities, which originate schizogenously, but later
become lysigenous owing to the dissolution of the outer layers of the
secretion cells.
[Illustration: PLATE 61
STALKED GLANDULAR HAIRS
1. Belladonna leaf (_Atropa belladonna_, L.).
2. Geranium stem (_Geranium maculatum_, L.).
3. Henbane leaf (_Hyoscyamus niger_, L.).
4. Tobacco leaf (_Nicotiana tabacum_, L.).]
SCHIZOGENOUS CAVITIES
=Schizogenous cavities= occur in white pine bark (Plate 62, Fig.
B). The cells lining the cavity are mostly tangentially elongated,
and the wall extends into the cavity in the form of a papillate
projection. Immediately back from these cells are two or three layers
of cells which resemble cortical parenchyma cells, except that they
are smaller and their walls are thinner.
In white pine bark there is a single layer of thin-walled cells
lining the cavity. Immediately surrounding the secretion cells is a
single layer of thick-walled fibrous cells.
In klip buchu (Plate 63, Fig. B), as in white pine leaf (Plate 64,
Fig. B), there is a single layer of thin-walled secretion cells which
are surrounded on three sides with parenchyma cells and on the outer
side by epidermal cells.
LYSIGENOUS CAVITIES
=Lysigenous cavities= occur on the rind of citrus fruits--bitter and
sweet orange, lemon, grapefruit, lime, etc., and in the leaves of
garden rue, etc.
In bitter orange peel, (Plate 64, Fig. A) the cavity is very
large, and the cells bordering the cavity are broken and partially
dissolved. The entire cells back of these are white, thin-walled,
tangentially elongated cells. There is a great variation in the size
of these cavities, the smaller cavities being the recently formed
cavities.
SCHIZO-LYSIGENOUS CAVITIES
=Schizo-lysigenous= cavities are formed in white pine bark and many
other plants owing to the increase in diameter of the stem. In such
cases the walls of the secreting cells break down. The resulting
cavity resembles lysigenous cavities.
=Unicellular secretion cavities= occur in ginger, aloe, calamus, and
in canella alba barb.
[Illustration: PLATE 62
_A._ Cross-section of calamus rhizome (_Acorus calamus_, L.). 1,
Intercellular space; 2, Parenchyma cells; 3, Secretion cavity.
_B._ Cross-section of white pine bark (_Pinus strobus_, L.). 1,
Parenchyma; 2, Secretion cavity; 3, Secretion cells.]
[Illustration: PLATE 63
_A._ Cross-section of a portion of canella alba bark (_Canella
alba_, Murr.). 1. Excretion cavity.
_B._ Cross-section of a portion of klip buchu leaf.
1. Epidermal cells.
2. Secretion cavity.
3. Secretion cells.]
[Illustration: PLATE 64
_A._ Cross-section of bitter orange peel (_Citrus aurantium_,
_amara_, L.). 1, Internal secretion cavity formed by the
dissolution of the walls of the central secreting cells; 2,
Secretion cells. _B._ Cross-section of white pine leaf (_Pinus
strobus_, L.). 1, Epidermal and hypodermal cells; 2, Parenchyma
cells with protruding inner walls; 3, Endodermis; 4, Secretion
cavity; 5, Secretion cells.]
In calamus (Plate 62, Fig. A) the cavity is larger than the
surrounding cells; it is rounded in outline, and it contains
oleoresin. These cavities are in contact with the ordinary parenchyma
cells, from which they are easily distinguished by their larger size
and rounded form.
The =unicellular oil cavity= of canella alba (Plate 63, Fig. A) is
rounded or oval in cross-section and is many times larger than the
surrounding cells. The wall, which is very thick, is of a yellowish
color.
Secretion cavities vary greatly in form, according to the part of the
plant in which they are found. In flower petals and leaves they are
spherical; in barks they are usually elliptical; in umbelliferous
fruits they are elongated and tube-like.
Mucilage cavities are not of common occurrence in medicinal plants.
They occur, however, in the stem and root bark of sassafras, the stem
bark of slippery elm, the root of althea, etc.
CHAPTER VIII
STORAGE TISSUE
Most drug plants contain storage products because they are
collected at a period of the year when the plant is storing, or has
stored, reserve products. These products are stored in a number of
characteristic ways and in different types of tissue.
The most important of the different types of storage tissue that
occurs in plants are the storage cells, the storage cavities, and the
storage walls.
STORAGE CELLS
Several different types of cells function as storage tissue. These
cells, which are given in the order of their importance, are
parenchyma, crystal cells, medullary rays, stone cells, wood fibres,
bast fibres, and epidermal and hypodermal cells.
CORTICAL PARENCHYMA
=Cortical parenchyma= of biennial rhizomes, bulbs, roots, and the
parenchyma of the endosperm of seeds store most of the reserve
economic food products of the higher plants.
=Pith parenchyma= of sarsaparilla root (Plate 65, Fig. 4) and
the pith parenchyma of the rhizome of memspermun, like the pith
parenchyma of most plants, function as storage cells.
WOOD PARENCHYMA
=Wood parenchyma=, particularly of the older wood, function as
storage tissue. The wood parenchyma of quassia, like the wood
parenchyma of most woods, contain stored products. In some cases the
wood parenchyma contain starch, in others crystals, and in others
coloring matter, etc.
[Illustration: PLATE 65
1. Stone cells with starch of Ceylon cinnamon (_Cinnamomum
ceylanicum_, Nees.). 2. Stone cells with solitary crystals of
calumba root (_Jateorhiza palmata_, [Lam.] Miers). 3. Parenchyma
cells, with starch of cascarilla bark (_Croton eluteria_, [L.]
Benn.). 4. Cortical parenchyma with starch of sarsaparilla root
(_Smilax officinalis_, Kunth). 5. Cortical parenchyma, with
starch of leptandra rhizome (_Leptandra virginica_, [L.] Nutt.).
6. Crystal cells, with solitary crystals of quebracho bark
(Schlechtendal). 7. Bast fibre of blackberry root with starch
(_Rubus cuneifolius_, Pursh.).]
[Illustration: PLATE 66
MUCILAGE AND RESIN
1. Cross-section of elm bark (_Ulmus fulva_, Michaux) showing two
cavities filled with partially swollen mucilage.
2. Mucilage mass from sassafras stem bark (_Sassafras variifolium_,
L.).
3. Mucilage mass from elm bark.
4. Resin mass from white pine bark (_Pinus strobus_, L.).]
In many plants, however, the parenchyma cells contain crystals. The
parenchyma cells of rhubarb contain rosette crystals, while the
parenchyma cells of the cortex of sarsaparilla and false unicorn root
contain bundles of raphides. In every case observed the raphides are
surrounded by mucilage. This is true of squills, sarsaparilla, false
unicorn, etc. When cells with raphides and mucilage are mounted in a
mixture of alcohol, glycerine, and water, the mucilage first swells
and finally disappears.
STORAGE CAVITIES
Particular attention should be given to =storage cavities= whenever
they occur in plants, for the reason that they are usually filled
with storage products, and for the added reason that storage cavities
are not common to all plants. Storage cavities occur in roots, stems,
leaves, flowers, fruits, and seeds.
CRYSTAL CAVITIES
Characteristic =crystal cavities= occur in many plants. Such a cavity
containing a bundle of raphides is shown in the cross-section of
skunk cabbage leaf (Plate 67).
SECRETION CAVITIES
In white pine bark there are a great number of secretion cavities
which are partially or completely filled with oleoresin. In the
cross-sections of white pine bark the secretion cavities are very
conspicuous, and they vary greatly in size. This variation is due,
first, to the age of the cavity, the more recently formed cavities
being smaller; and secondly, to the nature of the section, which will
be longer in longitudinal section, which will be through the length
of the secretion cavity, and shorter on transverse section. Such a
section shows the width of the secretion cavity.
Characteristic =mucilage cavities= occur in sassafras root, stem
bark, elm bark (Plate 66, Fig. 1), marshmallow root, etc. These
cavities form a conspicuous feature of the cross-section of these
plants. The presence or absence of mucilage cavities in a bark should
be carefully noted.
LATEX CAVITIES
The =latex tube cavities= are characteristic in the plants in which
they occur. These cavities as explained under latex tubes are very
irregular in outline.
[Illustration: PLATE 67
CROSS-SECTION OF SKUNK-CABBAGE LEAF (_Symplocarpus fœtidus_,
[L.] Nutt.)
1. Crystal cavity.
2. Bundle of raphides.]
OIL CAVITY
Canella alba contains an =oil cavity= resembling in form the mucilage
cavity of elm bark.
=Secretion cavities= occur in most of the umbelliferous fruits. For
each fruit there is a more or less constant number of cavities. Anise
has twenty or more, fennel usually has six cavities, and parsley has
six cavities.
In poison hemlock fruits there are no secretion cavities. In certain
cases, however, the number of secretion cavities can be made to vary.
This was proved by the author in the case of celery seed. He found
that cultivated celery seed, from which stalks are grown, contains
six oil cavities (Plate 122, Fig. 2), while wild celery seed (Plate
102, Fig. 1), grown for its medicinal value, always contains more
than six cavities. Most of the wild celery seeds contain twelve
cavities.
Many leaves contain cavities for storing secreted products. Such
storage cavities occur in fragrant goldenrod, buchu, thyme, savary,
etc.
The leaves in which such cavities occur are designated as
pellucid-punctate leaves. Such leaves will, when held between the eye
and the source of light, exhibit numerous rounded translucent spots,
or storage cavities.
GLANDULAR HAIRS
The =glandular hair of peppermint= (Plate 60, Fig. 3) and other mints
consists of eight secretion cells, arranged around a central cavity
and an outer wall which is free from the secretion cells. This outer
wall becomes greatly distended when the secretion cells are active,
and the space between the secretion cells and the wall serves as the
storage place for the oil. When the mints are collected and dried,
the oil remains in the storage cavity for a long time.
STONE CELLS
The =stone cells= of the different cinnamons (Plate 65, Fig. 1) store
starch grains; these grains often completely fill the stone cells.
The yellow stone cells of calumba root (Plate 65, Fig. 2) usually
contain four prisms of calcium oxalate, which may be nearly uniform
or very unequal in size.
BAST FIBRES
The =bast fibres= of the different rubus species (Plate 65, Fig. 7)
contain starch. The medullary rays of quassia (Plate 107, Fig. 2)
contain starch; while the medullary rays of canella alba contain
rosette crystals. In a cross-section of canella alba (Plate 81, Fig.
3) the crystals form parallel radiating lines which, upon closer
examination, are seen to be medullary rays, in each cell of which a
crystal usually occurs.
The =epidermal and hypodermal cells of leaves= serve as water-storage
tissue. These cells usually appear empty in a section.
The barks of many plants--_i.e._, quebracho, witch-hazel,
cascara, frangula, the leaves of senna and coca, and the root of
licorice--contain numerous crystals. These crystals occur in special
storage cells--=crystal cells= (Plate 65, Fig. 6)--which usually form
a completely enveloping layer around the bast fibres. These cells are
usually the smallest cells of the plant in which they occur, and with
but few exceptions each cell contains but a single crystal.
The epidermal cells of senna leaves and the epidermal cells of
mustard are filled with mucilage; the walls even consist of mucilage.
Such cells are always diagnostic in powders.
STORAGE WALLS
=Storage walls= (Plates 68 and 69) occur in colchicum seed, saw
palmetto seed, areca nut, nux vomica, and Saint Ignatius’s bean. In
each of these seeds the walls are strongly and characteristically
thickened and pitted. In no two plants are they alike, and in each
plant they are important diagnostic characters.
Storage cell walls consist of reserve cellulose, a form of cellulose
which is rendered soluble by ferments, and utilized as food during
the growth of the seed. Reserve cellulose is hard, bony, and of a
waxy lustre when dry. Upon boiling in water the walls swell and
become soft.
The structure of the reserve cellulose varies greatly in the
different seeds in which it occurs in the thickness of the walls and
in the number and character of the pores.
[Illustration: PLATE 68
RESERVE CELLULOSE
1. Saw palmetto (_Serenoa serrulata_, [Michaux] Hook., f.).
2. Areca nut (_Areca catechu_, L.).
3. Colchicum seed (_Colchicum autumnale_, L.).
3-_A_. Porous side wall.
3-_B_. Cell cavity above the side wall.]
[Illustration: PLATE 69
RESERVE CELLULOSE
1. Endosperm of nux vomica (_Strychnos nux vomica_, L.).
2. Endosperm of St. Ignatia bean (_Strychnos ignatii_, Berg.).]
CHAPTER IX
CELL CONTENTS
The cell contents of the plant are divided into two groups: first,
organic cell contents; and secondly, inorganic cell contents.
The =organic= cell contents include plastids, starch grains,
mucilage, inulin, sugar, hesperidin, alkaloids, glucocides, tannin,
resin, and oils.
CHLOROPHYLL
The =chloroplasts= of the higher plants are green, and they vary
somewhat in size, but they have a similar structure and form.
Chloroplasts are mostly oval in longitudinal view and rounded in
cross-section view. Each chlorophyll grain has an extremely thin
outer wall, which encloses the protoplasmic substance, the green
granules, a green pigment (chlorophyll), and a yellow pigment
(xanthophyll). Frequently the wall includes starch, oil drops, and
protein crystals.
Chloroplasts are arranged either in a regular peripheral manner along
the walls, or they are diffused throughout the protoplast.
The palisade cells of most leaves are packed with chlorophyll grains.
In the mesophyll cells the chlorophyll grains are not so numerous,
and they are arranged peripherally around the innermost part of the
wall.
Chloroplasts multiply by fission--that is, each chloroplast divides
into two equal halves, each of which develops into a normal
chloroplast.
Chlorophyll occurs in the palisade, spongy parenchyma, and guard
cells of the leaf; in the collenchyma and parenchyma of the cortex
of the stems of herbs and of young woody stems, and, under certain
conditions, in rhizomes and roots exposed to light. Almost without
exception young seeds and fruits have chlorophyll.
In powdered leaves, stems, etc., the chlorophyll grains occur in the
cells as greenish, more or less structureless masses. Yet cells with
chlorophyll are readily distinguished from cells with other cell
contents. In witch-hazel leaf the chlorophyll grains appear brownish
in color. Powdered leaves and herbs are readily distinguished from
bark, wood, root, and flower powders.
Leaves and the stems of herbs are of a bright-green color. With the
exception of the guard cells, the chloroplasts occur one or more
layers below the epidermis; but, owing to the translucent nature of
the outer walls of these cells, the outer cells of leaves and stems
appear green.
Wild cherry, sweet birch, and, in fact, most trees with smooth barks
have =chloroplasts= in several of the outer layers of the cortical
parenchyma. When the thin outer bark is removed from these plants,
the underlying layers are seen to be of a bright-green color.
LEUCOPLASTIDS
=Leucoplastids=, or colorless plastids, occur in the underground
portions of the plant; they may, when these organs in which they
occur are exposed to light, change to chloroplastids.
Leucoplasts are the builders of starch grains. They take the chemical
substance starch and build or mould it into starch grains, storage
starch, or reserve starch.
Other characteristic chromoplasts found in plants are yellow and
red. Yellow chromoplasts occur in carrot root and nasturtium flower
petals. Red plastids occur in the ripe fruit of capsicum.
STARCH GRAINS
The chemical substance starch (C₆H₁₀O₅) is formed in chloroplasts.
The starch thus formed is removed from the chloroplasts to other
parts of the plant because it is the function of the chloroplasts to
manufacture and not to store starch.
The starch formed by the chloroplasts is acted upon by a ferment
which adds one molecule of water to C₆H₁₀O₅, thus forming sugar
C₆H₁₂O₆. This sugar is readily soluble in the cell sap, and is
conducted to all parts of the plant. The sugar not utilized in cell
metabolism is stored away in the form of reserve starch or starch
grains by colorless plastids or amyloplasts.
The amyloplasts change the sugar into starch by extracting a molecule
of water. This structureless material (starch) is then formed by the
amyloplast into starch grains having a definite and characteristic
form and structure.
Starch grams vary greatly in different species of plants, owing
probably to the variation of the chemical composition, density, etc.,
of the protoplast, and to the environmental conditions under which
the plant is growing.
OCCURRENCE
Starch grains are simple, compound, or aggregate. =Simple starch=
grains may occur as isolated grains (Plates 70, 71, and 72), or they
may be associated as in cardamon seed, white pepper, cubeb, and
grains of paradise, where the simple grains stick together in masses,
having the outline of the cells in which they occur. These masses are
known as aggregate starch.
=Aggregate starch= (Plate 76) varies greatly in size, form, and in
the nature of the starch grains forming the aggregations.
=Compound starch grains= may be composed of two or more parts, and
they are designated as 2, 3, 4, 5, etc., compound (Plate 75).
The parts of a compound grain may be of equal size (Plate 75, Fig.
4), or they may be of unequal size (Plate 75, Fig. 2).
In most powders large numbers of the parts of the compound grains
become separated. The part in contact with other grains shows plane
surfaces, while the external part of the grain has a curved surface.
There will be one plane and one curved surface if the grain is a half
of a two-compound grain; two plane and one curved surface if the
grain is a part of a three-compound grain, etc.
The simple starch grains forming the aggregations become separated
during the milling process and occur singly, so that in the drugs
cited above the starch grains are solitary and aggregate.
Many plants contain both simple and compound starch grains (Plate 74,
Fig. 3).
In some forms--_e.g._, belladonna root (Plate 75, Fig. 2) the
compound grains are more numerous; while in sanguinaria the simple
grains are more numerous, etc.
OUTLINE
The =outline= of starch grains is made up of (1) rounded, (2) angled,
and (3) rounded and angled surfaces.
Starch grains with rounded surfaces may be either spherical, as in
Plate 74, Fig. 3, or oblong or elongated, as in Plate 71, Fig. 1.
Other starches with rounded surfaces are shown on Plates 72 and 73.
Angled outlined grains are common to cardamon seed, white pepper,
cubebs, grains of paradise (Plate 76, Fig. 4), and to corn (Plate 70,
Fig. 3).
The outlines of all compound grains are made up partly of plane and
partly of curved surfaces.
SIZE
The =size= (greatest diameter) of starch varies greatly even in the
same species, but for each plant there is a normal variation.
In spherical starch grains the size of the individual grains is
invariable, but in elongated starch grains and in parts of compound
grains the size will vary according to the part of the grain
measured. In zedoary starch (Plate 71, Fig. 4), for instance, the
size will vary according to whether the end, side, or surface of the
starch grain is in focus.
The parts of compound grains often vary greatly in size. Such a
variation is shown in Plate 75, Fig. 2.
HILUM
The =hilum= is the starting-point of the starch grain or the first
part of the grain laid down by the amyloplast. The hilum will be
central if formed in the middle of the amyloplast, and excentral if
formed near the surface of the amyloplast. It has been shown that the
developing starch grain with eccentric hilum usually extends the wall
of the amyloplast if it does not actually break through the wall.
Starch grains with excentral hilums are therefore longer than broad.
[Illustration: PLATE 70
STARCH
1. Calabar bean (_Physostigma venenosum_, Balfour).
2. Marshmallow root (_Althæa officinalis_, L.).
3. Field corn (_Zea mays_, L.).]
[Illustration: PLATE 71
STARCH
1. Galanga root (_Alpinia officinarum_, Hance). 2. Kola nut (_Cola
vera_, [K.] Schum.). 3. Geranium rhizome (_Geranium maculatum_ L.).
4. Zedoary root (_Curcuma zedoaria_, Rosc.). 4-_A_. Surface view of
starch grain. 4-_B_. Side view of starch grain. 4-_C_. End view of
starch grain.]
In central hilum starch grains the grain is laid down around the
hilum in the form of concentric layers. These layers are of variable
density. The dense layers are formed when plenty of sugar is
available, and the less dense layers are formed when little sugar
is available. The unequal density of the different layers gives the
striated appearance characteristic of so many starch grains.
In eccentric hilum starch grains the starch will be deposited in
layers which are outside of and successively farther from the hilum.
The term _hilum_ has come to have a broader meaning than formerly.
Hilum includes at the present time not only the starting-point of the
starch grain, but the fissures which form in the grain upon drying.
In all cases these fissures originate in the starting-point, hilum,
and in some cases extend for some distance from it. The hilum, when
excentral, may occur in the broad end of the grain, galanga, and
geranium (Plate 71, Figs, 1 and 3), or in the narrow end of the
grain, zedoary (Plate 71, Fig. 4).
NATURE OF THE HILUM
The hilum, whether central or excentral, may be rounded (Plate 75,
Fig. 1); or simple cleft, which may be straight (Plate 71, Fig. 1);
or curved cleft (Plate 71, Fig. 2); or the hilum may be a multiple
cleft (Plate 74, Fig. 3).
In studying starches use cold water as the mounting medium, because
in cold water the form and structure are best shown, and because
there is no chemical action on the starch. On the other hand, the
form and structure will vary considerably if the starch is mounted
in hot water or in solutions of alkalies or acids. The hilum appears
colorless when in sharp focus, and black when out of focus.
Starch grains, when boiled with water, swell up and finally
disintegrate to form starch paste.
Starch paste turns blue upon the addition of a few drops of weak
Lugol solution. Upon heating, this blue solution is decolorized, but
the color reappears upon cooling. If a strong solution of Lugol is
used in testing, the color will be bluish black.
[Illustration: PLATE 72
STARCH
1. Orris root (_Iris florentinia_ L.).
2. Stillingia root (_Stillingia sylvatica_, L.).
3. Calumba root (_Jateorhiza palmata_, [Lam.] Miers.).]
[Illustration: PLATE 73
STARCH
1. Male fern (_Dryopteris marginalis_, [L.] A. Gray).
2. African ginger (_Zingiber officinalis_, Rosc.).
3. Yellow dock (_Rumex crispus_, L.).
4. Pleurisy root (_Asclepias tuberosa_, L.).]
[Illustration: PLATE 74
STARCH
1. Kava-kava (_Piper methysticum_, Forst., f.).
2. Pokeroot (_Phytolacca americana_, L.).
3. Rhubarb (_Rheum officinale_, Baill.).]
[Illustration: PLATE 75
STARCH GRAINS
1. Bryonia (_Bryonia alba_, L.).
2. Belladonna root (_Atropa belladonna_, L.).
3. Valerian root (_Valeriana officinalis_, L.).
4. Colchicum root (_Colchicum autumnale_, L.).]
[Illustration: PLATE 76
STARCH MASSES
1. Aggregate starch of cardamon seed (_Elettaria cardamomum_,
Maton).
2. Aggregate starch of white pepper (_Piper nigrum_, L.).
3. Aggregate starch of cubebs (_Piper cubeba_, L., f.).
4. Aggregate starch of grains of paradise (_Amomum melegueta_,
Rosc.).]
INULIN
=Inulin= is the reserve carbohydrate material found in the plants of
the composite family.
The medicinal plants containing inulin are dandelion, chicory,
elecampane, pyrethrum, and burdock. Plate 77, Figs, 1 and 2 show
masses of inulin in dandelion and pyrethrum.
In these plants the inulin occurs in the form of irregular,
structureless, grayish-white masses (Plate 77). In powdered drugs
inulin occurs either in the parenchyma cell or as irregular isolated
fragments of variable size and form. Inulin is structureless and the
inulin from one plant cannot be distinguished microscopically from
the inulin of another plant. For this reason inulin has little or no
diagnostic value. The presence or absence of inulin should always be
noted, however, in examining powdered drugs, because only a few drugs
contain inulin.
When cold water is added to a powder containing inulin it dissolves.
Solution will take place more quickly, however, in hot water.
Inulin occurs in the living plant in the form of cell sap. If fresh
sections of the plant are placed in alcohol or glycerine, the inulin
precipitates in the form of crystals.
MUCILAGE
=Mucilage= is of common occurrence in medicinal plants.
Characteristic mucilage cavities filled with mucilage occur in
sassafras stem (Plate 66, Fig. 2), in elm bark (Plate 66, Fig. 1), in
althea root, in the outer layer of mustard seed, and in the stem of
cactus grandiflorus. In addition, mucilage is found associated with
raphides in the crystal cells of sarsaparilla, squill, false unicorn,
and polygonatum.
When drugs containing mucilage are added to alcohol, glycerine, and
water mixture, the mucilage swells slightly and becomes distinctly
striated, but it will not dissolve for a long time. Refer to Plate
79, Fig. 6.
Mucilage, when associated with raphides, swells and rapidly dissolves
when added to alcohol, glycerine, and water mixture. The mucilage is,
therefore, different from the mucilage found in mucilage cavities,
because it is more readily soluble.
[Illustration: PLATE 77
INULIN (_Inula helenium_, L.)
1. Inulin in the parenchyma cells of dandelion root.
2. Inulin from Roman pyrethrum root (_Anacyclus pyrethrum_, [L.] D.
C.). ]
In coarse-powdered bark and other mucilage containing drugs the
mucilage masses are mostly spherical or oval in outline (Plate 66,
Figs. 2 and 3) the form being similar to the cavity in which the mass
occurs.
Acacia, tragacanth, and India gum consist of the dried mucilaginous
excretions.
HESPERIDIN
=Hesperidin= occurs in the epidermal cells of short and long buchu.
It is particularly characteristic in the epidermal cells of the dried
leaves of short buchu. In these leaves the hesperidin occurs in
masses which resemble rosette crystals (Plate 54, Fig. 1).
Hesperidin is insoluble in glycerine, alcohol, and water, but it
dissolves in alkali hydroxides, forming a yellowish solution.
VOLATILE OILS
=Volatile oils= occur in cinnamon stem bark, sassafras root bark,
flowers of cloves, and in the fruits of allspice, anise, fennel,
caraway, coriander, and cumin.
In none of these cases is the volatile oil diagnostic, but its
presence must always be determined.
When a powdered drug containing a volatile oil is placed in alcohol,
glycerine, and water mixture the volatile oil contained in the
tissues will accumulate at the broken end of the cells in the form of
rounded globules, while the volatile oil adhering to the surface of
the fragments will dissolve in the mixture and float in the solution
near the under side of the cover glass. Volatile oil is of little
importance in histological work.
TANNIN
=Tannin= masses are usually red or reddish brown. Tannin occurs in
cork cells, medullary rays of white pine bark (Plate 48, Fig. B),
stone cells, and in special tannin sacs.
The stone cells of hemlock and tamarac bark and the medullary rays of
white pine and hemlock bark contain tannin.
Tannin associated with prisms occurs in tannin sacs in white pine and
tamarac bark. These sacs are frequently several millimeters in length
and contain a great number of crystals surrounded by tannin.
Deposits of tannin are colored bluish black with a solution of ferric
chloride.
ALEURONE GRAINS
=Aleurone grains= are small granules of variable structure, size,
and form, and they are composed of reserve proteins. They occur in
celery, fennel, coriander, and anise, fruits, in sesame, sunflower,
curcas, castor oil, croton oil, bitter almond, and other oil seeds.
In many of the seeds the aleurone grains completely fill the cells of
the endosperm, embryo, and perisperm. In wheat, rye, barley, oats,
and corn the aleurone grains occur only in the outer layer or layers
of the endosperm, the remaining layers in these cases being filled
with starch.
In powdered drugs the aleurone grains occur in parenchyma cells or
free in the field.
STRUCTURE OF ALEURONE GRAINS
Aleurone grains are very variable in structure. The simplest grains
consist of an undifferentiated mass of proteid substance surrounded
by a thin outer membrane. In other grains the proteid substance
encloses one or more rounded denser proteid bodies known as globoids.
In other grains a crystalloid--crystal-like proteid substance--is
present in addition to the globoid. In some grains are crystals
of calcium oxalate, which may occur as prisms or as rosettes. All
the different parts, however, do not occur in any one grain. In
castor-oil seed (Plate 77_a_, Fig. 8) are shown the membrane (_A_),
the ground mass (_B_), the crystalloid (_C_), and the globoid (_D_).
FORM OF ALEURONE GRAINS
Much attention has been given to the study of the special parts
of the aleurone grains, but one of the most important diagnostic
characters has been overlooked, namely, that of comparative form. For
the purposes of comparing the forms of different grains, they should
be mounted in a medium in which the grain and its various parts are
insoluble. Oil of cedar is such a medium. The variation in form and
size of the aleurone grains when mounted in oil of cedar is shown in
Plate 77_a_.
DESCRIPTION OF ALEURONE GRAINS
The aleurone grains of curcas (Plate 77_a_, Fig. 1) vary in form
from circular to lens-shaped, and each grain contains one or more
globoids. The globoids are larger when they occur singly. In
sunflower seed (Plate 77_a_, Fig. 2) the grains vary from reniform to
oval, and one or more globoids are present; many occur in the center
of the grain.
The aleurone grains of flaxseed (Plate 77_a_, Fig. 3) resemble in
form those of sunflower seed, but the grains are uniformly larger and
some of the grains contain as many as five globoids.
In bitter almond (Plate 77_a_, Fig. 4) the aleurone grains are mostly
circular, but a few are nearly lens-shaped. A few of the large,
rounded grains contain as many as nine globoids; in such cases one
of the globoids is likely to be larger than the others. The aleurone
grains of croton-oil seed (Plate 77_a_, Fig. 5) are circular in
outline, variable in form, and each grain contains from one to seven
globoids.
In sesame seed (Plate 77_a_, Fig. 6) the typical grain is angled in
outline and the large globoid occurs in the narrow or constricted end.
The aleurone grains of castor-oil seed (Plate 77_a_, Fig. 7) resemble
those of sesame seed, but they are much larger, and many of the
grains contain three large globoids. When these grains are mounted in
sodium-phosphate solution, the crystalloid becomes visible.
TESTS FOR ALEURONE GRAINS
Aleurone grains are colored yellow with nitric acid and red with
Millon’s reagent.
The proteid substance of the mass of the grain, of the globoid, and
of the crystalloid, reacts differently with different reagents and
dyes.
The ground substance and the crystalloids are soluble in dilute
alkali, while the globoids are insoluble in dilute alkali.
The ground substance and crystalloids are soluble in sodium
phosphate, while the globoids are insoluble in sodium phosphate.
Calcium oxalate is insoluble in alkali and acetic acid, but it
dissolves in hydrochloric acid.
[Illustration: PLATE 77_a_
ALEURONE GRAINS
1. Curcas (_Jatropha curcas_, L.).
2. Sunflower seed (_Helianthus annuus_, L.).
3. Flaxseed (_Linum usitatissimum_, L.).
4. Bitter almond (_Prunus amygdalus_, _amara_, D.C.).
5. Croton-oil seed (_Croton tiglium_, L.).
6. Sesame seed (_Sesamum indicum_, L.).
7 and 8. Castor-oil seed (_Ricinus communis_, L.).]
CRYSTALS
Calcium oxalate crystals form one of the most important inorganic
cell contents found in plants, because of the permanency of the
crystals, and because the forms common to a given species are
invariable. By means of calcium oxalate crystals it is possible to
distinguish between different species. In butternut root bark, for
instance, only rosette crystals are found, while in black walnut
root bark--a common substitute for butternut bark--both prisms and
rosettes occur. This is only one of the many examples which could be
cited.
These crystals, for purposes of study, will be grouped into four
principal classes, depending upon form and not upon crystal system.
These classes are micro-crystals, raphides, rosettes, and solitary
crystals.
MICRO-CRYSTALS
=Micro-crystals= are the smallest of all the crystals. Under the
high power of the microscope they appear as a V, a Y, an X, and as
a T. They are, therefore, three- or four-angled (Plate 78). The
thicker portions of these crystals are the parts usually seen, but
when a close observation of the crystals is made the thin portions
of the crystal connecting the thicker parts may also be observed.
Micro-crystals should be studied with the diaphragm of the microscope
nearly closed and with the high-power objective in position. While
observing the micro-crystals, raise and lower the objective by the
fine adjustment in order to bring out the structure of the crystal
more clearly. Micro-crystals occur in parenchyma cells of belladonna,
scopola, stramonium, and bittersweet leaves; in belladonna, in
horse-nettle root, in scopola rhizome, in bittersweet stems, and in
yellow and red cinchona bark, etc.
The crystals in each of the above parts of the plant are similar in
form, the only observed variation being that of size. Their presence
or absence should always be noted when studying powders.
RAPHIDES
=Raphides=, which are usually seen in longitudinal view, resemble
double-pointed needles. They are circular in cross-section, and the
largest diameter is at the centre, from which they taper gradually
toward either end to a sharp point.
[Illustration: PLATE 78
MICRO-CRYSTALS
1. Horse-nettle root (_Solanum carolinense_, L.).
2. Scopola rhizome (_Scopolia carniolica_, Jacq.).
3. Belladonna root (_Atropa belladonna_, L.).
4. Bittersweet stem (_Solanum dulcamara_, L.).
5. Scopola leaf (_Scopola carniolica_, Jacq.).
6. Tobacco leaf (_Nicotiana tabacum_, L.).
7. Belladonna leaf (_Atropa belladonna_, L.).]
Raphides occur in bundles, as in false unicorn root (Plate 79, Figs.
6, A, B, and C), rarely as solitary crystals.
In ipecac root the crystals are usually solitary. In sarsaparilla
root, squill, etc., the raphides occur both in clusters, part of
bundle, or in bundles, and as solitary crystals.
In most drugs the crystals are entire; but in squills, where the
raphides are very large, they are broken. In phytolacca (Plate 79,
Fig. 1) and in hydrangea the raphides are usually broken, owing to
the fact that these drugs contain large quantities of fibres which
break them up into fragments when the drug is milled.
There is the greatest possible variation in the size of raphides in
the same and in different drugs, but the larger forms are constant in
the same species.
Raphides are deposited in parenchyma cells and in special raphides
sacs. These crystals are always surrounded with mucilage.
ROSETTE CRYSTALS
=Rosette crystals= are compound crystals composed of an aggregation
of small crystals arranged in a radiating manner around a central
core. This core appears nearly black, and the whole mass is nearly
spherical. The free ends of the crystals are sharp-pointed or blunt.
Characteristic rosette crystals occur in frangula bark, spikenard
root, wahoo stem, root bark, rhubarb, etc. (Plate 80, Figs. 1, 2, 3,
4, 5, and 6).
These crystals are very variable in size. This variation is
illustrated by the crystals of Plate 80.
Usually there is a variation in size of the crystals occurring in
a given plant, but for each plant there is a more or less uniform
variation. For instance, the largest rosette crystal occurring in
wahoo root bark (Plate 80, Fig. 5) is smaller than the largest
crystal occurring in rhubarb (Plate 80, Fig. 6), etc.
[Illustration: PLATE 79
RAPHIDES
1. Phytolacca root (_Phytolacca americana_, L.). 2. Squills
(_Urginea maritima_ [L.] Baker). 3. Hydrangea root (_Hydrangea
arborescens_, L.). 4. Convallaria (_Convallaria majalis_, L.).
5. Carthagean ipecac (_Cephælis acuminata_ Karst.) 6. Bundle of
raphides from false unicorn root.
_A._ Bundle surrounded with mucilage. _B._ Mucilage expanded and
partially dissolved. _C._ Bundle free of mucilage.]
[Illustration: PLATE 80
ROSETTE CRYSTALS
1. Frangula bark (_Rhamnus frangula_, L.).
2. White oak bark (_Quercus alba_, L.).
3. Spikenard root (_Aralia racemosa_, L.).
4. Wahoo stem bark (_Euonymus atropurpureus_, Jacq.).
5. Wahoo root bark (_Euonymus atropurpureus_, Jacq.).
6. Rhubarb (_Rheum officinale_, Baill.).]
The prisms forming the rosette crystals, like all prisms, decompose
white light, with the result that rosette crystals frequently appear
variously colored. Rhubarb crystals, for instance, are blue or
violet. Most of the smaller rosette crystals, however, appear grayish
white with a darker-colored centre.
Rosette crystals occur in parenchyma cells (Plate 81, Fig. 4) and in
medullary rays (Plate 81, Fig. 3).
SOLITARY CRYSTALS
=Solitary crystals= are the most variable of all the forms of calcium
oxalate. They usually occur in crystal cells associated with bast
fibres and stone cells, less frequently in stone cells (Plate 33,
Fig. 2). There are many different and characteristic forms of prisms.
The more common are:
1. Rectangular:
A. Parallelepipeds.
B. Cubes.
2. Polyhedrons:
A. Irregular polyhedrons.
I. Flat bases.
(_a_) Non-notched.
(_b_) Notched.
II. Tapering bases.
B. Octohedrons.
The crystals occurring in Batavia cinnamon and henbane leaves are
parallelopipeds (Plate 82, Figs. 1 and 2).
The crystals occurring in cactus grandiflorus, hemlock bark, krameria
root, and soap bark are irregular polyhedrons (Plate 83). They
are longer than broad, and the ends are tapering. The crystal of
cactus grandiflorus has the narrowest diameter of these four, while
the crystals of soap bark have the widest diameter. In coca leaf,
xanthoxylum bark, elm bark, Spanish licorice, and in white oak (Plate
84), and in cocillina bark (Plate 82, Fig. 4) the crystals are all
irregular polyhedrons with flat bases. They are mostly longer than
broad and they are all widest in the centre; in each a few crystals
are notched, but most of the crystals are not notched.
The crystals in quassia wood, uva-ursi leaf, and most of those of
quebracho and wild cherry bark (Plate 86, Figs. 1, 2, 3, and 4) are
irregular polyhedrons with flat ends. They are longer than broad,
widest at the centre, and non-notched.
[Illustration: PLATE 81
INCLOSED ROSETTE CRYSTALS
1. Hops (_Humulus lupulus_, L.).
2. Bracts of cannabis indica (_Cannabis sativa_, variety _Indica_,
Lamarck).
3. Medullary rays of canella alba.
4. Parenchyma cells of mandrake (_Podophyllum peltatum_, L.).]
[Illustration: PLATE 82
SOLITARY CRYSTAL
1. Batavia cinnamon (_Cinnamomum burmanni_, Nees).
2. Henbane leaves (_Hyoscyamus niger_, L.).
3. Morea nutgalls.
4. Cocillana bark (_Guarea rusbyi_ [Britton], Rusby).]
[Illustration: PLATE 83
SOLITARY CRYSTALS
1. Cactus grandiflorus (_Cereus grandiflorus_ [L.], Britton and
Rose).
2. Hemlock bark (_Tsuga canadensis_ [L.], Carr.).
3. Krameria root (_Krameria triandra_, Ruiz and Pav.).
4. Soapbark (_Quillaja saponaria_, Molina).]
[Illustration: PLATE 84
SOLITARY CRYSTALS
1. Coca leaf (_Erythroxylon coca_, Lamarck).
2. Xanthoxylum bark (_Zanthoxylum americanum_, Miller).
3. Elm bark (_Ulmus fulva_, Michaux).
4. Spanish licorice root (_Glycyrrhiza glabra_, L.).
5. White oak bark (_Quercus alba_, L.).]
Cubes occur in senna, cascara sagrada, frangula, white pine, tamarac
(Plate 85), quassia, uva-ursi, quebracho, and in wild cherry (Plate
86).
The crystals of morea nutgalls (Plate 82, Fig. 3) are octahedrons,
and they resemble the crystals of calcium oxalate found in urinary
sediments.
While studying the prisms, focus first on the upper surface and then
down to the under surface in order to observe the forms accurately.
There are several plants in which more than one form of crystal
occur. Rosette crystals and prisms are associated, for instance, in
cascara sagrada, frangula, condurango, dogwood, and pleurisy root
(Plate 87, Figs. 1, 2, 3, 4, and 5).
An important factor to be kept in mind in studying crystals is the
number--whether abundant, as in rhubarb, or sparingly present, as in
mandrake, etc. Variation in the number of crystals is not uncommon,
even in different parts of the same plants. In wahoo stem bark, for
instance, there are several times as many rosette crystals as there
are in the root bark.
Crystals of calcium oxalate are freely soluble in dilute hydrochloric
acid without effervescence; but they are insoluble in acetic acid and
in sodium and potassium hydroxide solutions. With sulphuric acid they
form crystals of calcium sulphate.
CYSTOLITHS
=Cystoliths= consist of calcium carbonate deposited over and around a
framework of cellulose.
FORMS OF CYSTOLITHS
The =forms of cystoliths= differ greatly in the different plants in
which they occur.
In the rubber-plant leaf, the cystolith resembles a bunch of grapes
and is stalked; in ruellia root (Plate 87, Fig. 1) the cystoliths
vary from nearly circular to narrowly cylindrical, and no stalk is
present; also the cystolith nearly fills the cell in which it occurs.
In the hair of cannabis indica (Plate 88, Fig. 3), the cystolith
varies in form according to the size and shape of the hair, but in
all the hairs the cystolith appears to be attached to the upper
curved part of the inner wall of the hair.
[Illustration: PLATE 85
SOLITARY CRYSTALS
1. India senna (_Cassia angustifolia_, Vahl.).
2. Cascara sagrada bark (_Rhamnus purshiana_, D. C.).
3. Frangula bark (_Rhamnus frangula_, L.).
4. White pine bark (_Pinus strobus_, L.).
5. Tamarac bark (_Larix laricina_ [Du Roi], Koch).]
[Illustration: PLATE 86
SOLITARY CRYSTALS
1. Quassia (_Picræna excelsa_ [Swartz.], Lindl.).
2. Uva-ursi leaf (_Arctostaphylos uva-ursi_ [L.], Spring.).
3. Quebracho bark (_Aspidosperma quebracho-blanco_, Schlechtendal).
4. Wild-cherry bark (_Prunus serotina_, Ehrh.).]
[Illustration: PLATE 87
ROSETTE CRYSTALS AND SOLITARY CRYSTALS OCCURRING IN
1. Cascara sagrada bark (_Rhamnus purshiana_, D.C.).
2. Frangula bark (_Rhamnus frangula_, L.).
3. Cundurango bark (_Marsdenia cundurango_, [Triana] Nichols).
4. Dogwood root bark (_Cornus florida_, L.).
5. Pleurisy root (_Asclepias tuberosa_, L.).]
[Illustration: PLATE 88
CYSTOLITHS
1. Ruellia root (_Ruellia ciliosa_, Pursh.).
2. Pellionia leaf.
3. Cannabis indica (_Cannabis sativa_, variety _Indica_, Lam.).]
Cystoliths occur, then, in special cavities, in parenchyma
cells (rubber-plant leaf, fig, pellionea, and mulberry), and in
non-glandular hairs (cannabis indica).
In powdered ruellia root the cystoliths occur in or are separated
from the parenchyma cells.
TESTS FOR CYSTOLITHS
When dilute hydrochloric acid or acetic acid is added to cystoliths a
brisk effervescence takes place with the evolution of carbon dioxide
gas.
Part III
HISTOLOGY OF ROOTS, RHIZOMES, STEMS,
BARKS, WOODS, FLOWERS, FRUITS,
AND SEEDS
In Part II the different types of cells and cell contents found in
plants have been studied. In Part III it will be shown how these
different cells are associated and the nature of the cell contents
in the different parts of the plant. These parts are the root, the
rhizome, the stem of herbs, bark and wood of woody stems, the leaf,
the flower, the fruit, and the seed.
CHAPTER I
ROOTS AND RHIZOMES
Some fifty-five roots, rhizomes, and rhizomes and roots are official
in the pharmacopœia and national formulary. About 5 of these are
obtained from monocotyledonous plants, and 50 from dicotyledonous
plants.
In studying the structure of roots and rhizomes, then, it must first
be determined whether the root in question is monocotyledonous or
dicotyledonous. This fact is ascertained by determining the type of
the fibro-vascular bundle. The bundle is of the open collateral type
in all rhizomes and roots obtained from monocotyledonous plants, but
it is closed, radial, or concentric in the monocotyledonous type.
In both of these groups the cellular plan of structure is similar,
the chief variation being the absence of one or more types of cells,
the variation in the amount, in arrangement, in the anatomical
structure, in the color, and in the cell contents of the individual
cells. These facts will be impressed on the mind while studying the
rhizomes and the roots.
CROSS-SECTION PINK ROOT
The cross-section of pink root (Plate 89) has the following structure:
=Epidermis.= The epidermal cells are small, nearly as long as broad,
and the outer wall is thicker and darker in color than the side and
inner walls. The cells usually contain air.
=Cortex.= The cortical parenchyma cells are very large and somewhat
rounded in outline, and the walls are white. There are about twelve
rows of these cells, and each cell contains numerous small, rounded
starch grains.
=Endodermis.= The endodermal cells are tangentially elongated, and
the walls are very thin and white. There are two or three layers of
endodermal cells; the cells’ outer layers are larger than the cells
of the inner layers.
[Illustration: PLATE 89
CROSS-SECTION OF ROOT OF SPIGELIA MARYLANDICA, L.
1. Epidermis. 2. Cortical parenchyma. 2´. Intercellular space. 3.
Endodermis. 4. Pericycle. 5. Cambium. 6. Xylem. 7. Pith.]
=Pericycle.= The cells forming the pericycle are sieve cells and
phloem parenchyma. The =sieve cells= are small, angled cells with
extremely thin, white walls.