CLASSIFICATION OF THE MONOCOTYLEDONS.
In the following chapter no attempt will be made to give an exhaustive
account of the characteristics of each division of the monocotyledons,
but only such of the most important ones as may serve to supplement
our study of the special one already examined. The classification
here, and this is the case throughout the spermaphytes, is based
mainly upon the characters of the flowers and fruits.
The classification adopted here is that of the German botanist
Eichler, and seems to the author to accord better with our present
knowledge of the relationships of the groups than do the systems that
are more general in this country. According to Eichler's
classification, the monocotyledons may be divided into seven groups;
viz., I. _Liliifloræ_; II. _Enantioblastæ_; III. _Spadicifloræ_;
IV. _Glumaceæ_; V. _Scitamineæ_; VI. _Gynandræ_; VII. _Helobiæ_.
ORDER I.--_Liliifloræ_.
The plants of this group agree in their general structure with the
adder's-tongue, which is a thoroughly typical representative of the
group; but nevertheless, there is much variation among them in the
details of structure. While most of them are herbaceous forms (dying
down to the ground each year), a few, among which may be mentioned the
yuccas ("bear grass," "Spanish bayonet") of our southern states,
develop a creeping or upright woody stem, increasing in size from year
to year. The herbaceous forms send up their stems yearly from
underground bulbs, tubers, _e.g._ _Trillium_ (Fig. 83, _A_), or
thickened, creeping stems, or root stocks (rhizomes). Good examples of
the last are the Solomon's-seal (Fig. 83, _B_), _Medeola_ (_C_, _D_),
and iris (Fig. 84 _A_). One family, the yams (_Dioscoreæ_), of which
we have one common native species, the wild yam (_Dioscorea villosa_),
have broad, netted-veined leaves and are twining plants, while another
somewhat similar family (_Smilaceæ_) climb by means of tendrils at the
bases of the leaves. Of the latter the "cat-brier" or "green-brier" is
a familiar representative.
[Illustration: FIG. 83.--Types of _Liliifloræ_. _A_, _Trillium_, × ¼.
_B_, single flower of Solomon's-seal (_Polygonatum_), × 1. _C_, upper
part of a plant. _D_, underground stem (rhizome) of Indian cucumber
root (_Medeola_), × ½. _E_, a rush (_Juncus_), × 1. _F_, a single
flower, × 2. _A-D_, _Liliaceæ_; _E_, _Juncaceæ_.]
The flowers are for the most part conspicuous, and in plan like that
of the adder's-tongue; but some, like the rushes (Fig. 83, _E_), have
small, inconspicuous flowers; and others, like the yams and smilaxes,
have flowers of two kinds, male and female.
[Illustration: FIG. 84.--Types of _Liliifloræ_. _A_, flower of the
common blue-flag (_Iris_), × ½ (_Iridaceæ_). _B_, the petal-like upper
part of the pistil, seen from below, and showing a stamen (_an._).
_st._ the stigma, × ½. _C_, the young fruit, × ½. _D_, section of the
same, × 1. _E_, diagram of the flower. _F_, part of a plant of the
so-called "gray moss" (_Tillandsia_), × ½ (_Bromeliaceæ_). _G_, a
single flower, × 2. _H_, a seed, showing the fine hairs attached to
it, × 1. _I_, plant of pickerel-weed (_Pontederia_), × ¼
(_Pontederiaceæ_). _J_, a single flower, × 1. _K_, section of the
ovary, × 4.]
The principal family of the _Liliifloræ_ is the _Liliaceæ_, including
some of the most beautiful of all flowers. All of the true lilies
(_Lilium_), as well as the day lilies (_Funkia_, _Hemerocallis_) of
the gardens, tulips, hyacinths, lily-of-the-valley, etc., belong here,
as well as a number of showy wild flowers including several species of
tiger-lilies (_Lilium_), various species of _Trillium_ (Fig. 83, _A_),
Solomon's-seal (_Polygonatum_) (Fig. 83, _B_), bellwort (_Uvularia_),
and others. In all of these, except _Trillium_, the perigone leaves
are colored alike, and the leaves parallel-veined; but in the latter
the sepals are green and the leaves broad and netted-veined. The fruit
of the _Liliaceæ_ may be either a pod, like that of the
adder's-tongue, or a berry, like that of asparagus or Solomon's-seal.
Differing from the true lilies in having the bases of the perigone
leaves adherent to the surface of the ovary, so that the latter is
apparently below the flower (inferior), and lacking the inner circle
of stamens, is the iris family (_Iridaceæ_), represented by the wild
blue-flag (_Iris versicolor_) (Fig. 84, _A_, _E_), as well as by
numerous cultivated species. In iris the carpels are free above and
colored like the petals (_B_), with the stigma on the under side. Of
garden flowers the gladiolus and crocus are the most familiar
examples, besides the various species of iris; and of wild flowers the
little "blue-eyed grass" (_Sisyrinchium_).
[Illustration: FIG. 85.--_Enantioblastæ_. _A_, inflorescence of the
common spiderwort (_Tradescantia_), × ½ (_Commelyneæ_). _B_, a single
stamen, showing the hairs attached to the filament, × 2. _C_, the
pistil, × 2.]
The blue pickerel-weed (_Pontederia_) is the type of a family of which
there are few common representatives (Fig. 84, _I_, _K_).
The last family of the order is the _Bromeliaceæ_, all inhabitants of
the warmer parts of the globe, but represented in the southern states
by several forms, the commonest of which is the so-called "gray moss"
(_Tillandsia_) (Fig. 84, _F_, _H_). Of cultivated plants the pineapple,
whose fruit consists of a fleshy mass made up of the crowded fruits
and the fleshy flower stalks, is the best known.
ORDER II.--_Enantioblastæ_.
The second order of the monocotyledons, _Enantioblastæ_, includes very
few common plants. The most familiar examples are the various species
of _Tradescantia_ (Fig. 88), some of which are native, others exotic.
Of the cultivated forms the commonest is one sometimes called
"wandering-jew," a trailing plant with zigzag stems, and oval, pointed
leaves forming a sheath about each joint. Another common one is the
spiderwort already referred to. In this the leaves are long and
pointed, but also sheathing at the base. When the flowers are showy,
as in these, the sepals and petals are different, the former being
green. The flowers usually open but once, and the petals shrivel up as
the flower fades. There are four families of the order, the spiderwort
belonging to the highest one, _Commelyneæ_.
ORDER III.--_Spadicifloræ_.
The third order of the monocotyledons, _Spadicifloræ_, is a very large
one, and includes the largest and the smallest plants of the whole
sub-class. In all of them the flowers are small and often very
inconspicuous; usually, though not always, the male and female flowers
are separate, and often on different plants. The smallest members of
the group are little aquatics, scarcely visible to the naked eye, and
of extremely simple structure, but nevertheless these little plants
produce true flowers. In marked contrast to these are the palms, some
of which reach a height of thirty metres or more.
The flowers in most of the order are small and inconspicuous, but
aggregated on a spike (spadix) which may be of very large size. Good
types of the order are the various aroids (_Aroideæ_), of which the
calla (_Richardia_) is a very familiar cultivated example. Of wild
forms the sweet-flag (_Acorus_), Jack-in-the-pulpit (_Arisæma_)
(Fig. 86, _A_, _D_), skunk-cabbage (_Symplocarpus_), and wild calla
may be noted. In _Arisæma_ (Fig. 86, _A_) the flowers are borne only
on the base of the spadix, and the plant is diœcious. The flowers are
of the simplest structure, the female consisting of a single carpel,
and the male of four stamens (_C_, _D_). While the individual flowers
are destitute of a perigone, the whole inflorescence (cluster of
flowers) is surrounded by a large leaf (spathe), which sometimes is
brilliantly colored, this serving to attract insects. The leaves of
the aroids are generally large and sometimes compound, the only
instance of true compound leaves among the monocotyledons (Fig. 86,
_B_).
[Illustration: FIG. 86.--Types of _Spadicifloræ_. _A_, inflorescence
of Jack-in-the-pulpit (_Arisæma_, _Aroideæ_). The flowers (_fl._) are
at the base of a spike (spadix), surrounded by a sheath (spathe),
which has been cut away on one side in order to show the flowers, × ½.
_B_, leaf of the same plant, × ¼. _C_, vertical section of a female
flower, × 2. _D_, three male flowers, each consisting of four stamens,
× 2. _E_, two plants of a duck-weed (_Lemna_), the one at the left is
in flower, × 4. _F_, another common species. _L_, _Trisulea_, × 1.
_G_, male flower of _E_, × 25. _H_, optical section of the female
flower, showing the single ovule (_ov._), × 25. _I_, part of the
inflorescence of the bur-reed (_Sparganium_), with female flowers, × ½
(_Typhaceæ_). _J_, a single, female flower, × 2. _K_, a ripe fruit,
× 1. _L_, longitudinal section of the same. _M_, two male flowers,
× 1. _N_, a pond-weed (_Potomogeton_), × 1 (_Naiadaceæ_). _O_, a
single flower, × 2. _P_, the same, with the perianth removed, × 2.
_Q_, fruit of the same, × 2.]
Probably to be regarded as reduced aroids are the duck-weeds
(_Lemnaceæ_) (Fig. 86, _F_, _H_), minute floating plants without any
differentiation of the plant body into stem and leaves. They are
globular or discoid masses of cells, most of them having roots; but
one genus (_Wolffia_) has no roots nor any trace of fibro-vascular
bundles. The flowers are reduced to a single stamen or carpel (Figs.
_E_, _G_, _H_).
The cat-tail (_Typha_) and bur-reed (_Sparganium_) (Fig. 86, _I_, _L_)
are common representatives of the family _Typhaceæ_, and the
pond-weeds (_Naias_ and _Potomogeton_) are common examples of the
family _Naiadeæ_. These are aquatic plants, completely submerged
(_Naias_), or sometimes partially floating (_Potomogeton_). The latter
genus includes a number of species with leaves varying from linear
(very narrow and pointed) to broadly oval, and are everywhere common
in slow streams.
The largest members of the group are the screw-pines (_Pandaneæ_) and
the palms (_Palmæ_). These are represented in the United States by
only a few species of the latter family, confined to the southern and
southwestern portions. The palmettoes (_Sabal_ and _Chamærops_) are
the best known.
Both the palms and screw-pines are often cultivated for ornament, and
as is well known, in the warmer parts of the world the palms are among
the most valuable of all plants. The date palm (_Phœnix dactylifera_)
and the cocoanut (_Cocos nucifera_) are the best known. The apparently
compound ("pinnate" or feather-shaped) leaves of many palms are not
strictly compound; that is, they do not arise from the branching of an
originally single leaf, but are really broad, undivided leaves, which
are closely folded like a fan in the bud, and tear apart along the
folds as the leaf opens.
Although these plants reach such a great size, an examination of the
stem shows that it is built on much the same plan as that of the other
monocotyledons; that is, the stem is composed of a mass of soft,
ground tissue through which run many small isolated, fibro-vascular
bundles. A good idea of this structure may be had by cutting across a
corn-stalk, which is built on precisely the same pattern.
ORDER IV.--_Glumaceæ_.
The plants of this order resemble each other closely in their habit,
all having long, narrow leaves with sheathing bases that surround the
slender, distinctly jointed stem which frequently has a hard, polished
surface. The flowers are inconspicuous, borne usually in close spikes,
and destitute of a perigone or having this reduced to small scales or
hairs. The flowers are usually surrounded by more or less dry leaves
(glumes, paleæ) which are closely set, so as to nearly conceal the
flowers. The flowers are either hermaphrodite or unisexual.
[Illustration: FIG. 87.--Types of _Glumaceæ_. _A_, a sedge, _Carex_
(_Cyperaceæ_). ♂, the male; ♀, the female flowers, × ½. _B_, a single
male flower, × 2. _C_, a female flower, × 2. _D_, fruiting spike of
another _Carex_, × ½. _E_, a single fruit, × 1. _F_, the same, with
the outer envelope removed, and slightly enlarged. _G_, section of
_F_, × 3. _em._ the embryo. _H_, a bulrush, _Scirpus_ (_Cyperaceæ_),
× ½. _I_, a single spikelet, × 2. _J_, a single flower, × 3. _K_, a
spikelet of flowers of the common orchard grass, _Dactylis_
(_Gramineæ_), × 2. _L_, a single flower, × 2. _M_, the base of a leaf,
showing the split sheath encircling the stem, × 1. _N_, section of a
kernel of corn, showing the embryo (_em._), × 2.]
There are two well-marked families, the sedges (_Cyperaceæ_) and the
grasses (_Gramineæ_). The former have solid, often triangular stems,
and the sheath at the base of the leaves is not split. The commonest
genera are _Carex_ (Fig. 87, _A_, _G_) and _Cyperus_, of which there
are many common species, differing very little and hard to
distinguish. There are several common species of _Carex_ which blossom
early in the spring, the male flowers being quite conspicuous on
account of the large, yellow anthers. The female flowers are in
similar spikes lower down, where the pollen readily falls upon them,
and is caught by the long stigmas. In some other genera, _e.g._ the
bulrushes (_Scirpus_) (Fig. 87, _H_), the flowers are hermaphrodite,
_i.e._ contain both stamens and pistils. The fruit (Fig. 87, _F_) is
seed-like, but really includes the wall of the ovary as well, which is
grown closely to the enclosed seed. The embryo is small, surrounded by
abundant endosperm (Fig. 87, _G_). Very few of the sedges are of any
economic importance, though one, the papyrus of Egypt, was formerly
much valued for its pith, which was manufactured into paper.
The second family, the grasses, on the contrary, includes the most
important of all food plants, all of the grains belonging here. They
differ mainly from the sedges in having, generally, hollow,
cylindrical stems, and the sheath of the leaves split down one side;
the leaves are in two rows, while those of the sedges are in three.
The flowers (Fig. 87, _L_) are usually perfect; the stigmas, two in
number and like plumes, so that they readily catch the pollen which is
blown upon them. A few, like the Indian corn, have the flowers
unisexual; the male flowers are at the top of the stem forming the
"tassel," and the female flowers lower down forming the ear. The
"silk" is composed of the enormously lengthened stigmas. The fruits
resemble those of the sedges, but the embryo is usually larger and
placed at one side of the endosperm (_N_, _em._).
While most of the grasses are comparatively small plants, a few of
them are almost tree-like in their proportions, the species of bamboo
(_Bambusa_) sometimes reaching a height of twenty to thirty metres,
with stems thirty to forty centimetres in diameter.
ORDER V.--_Scitamineæ_.
[Illustration: FIG. 88.--_Scitamineæ_. _A_, upper part of a flowering
plant of Indian shot (_Canna_), much reduced in size (_Cannaceæ_).
_B_, a single flower, × ½. _C_, the single stamen (_an._), and
petal-like pistil (_gy._), × 1. _D_, section of the ovary, × 2. _E_,
diagram of the flower. The place of the missing stamens is indicated
by small circles. _F_, fruit, × ½. _G_, section of an unripe seed.
_em._ embryo. _p_, perisperm, × 2.]
The plants of this order are all inhabitants of the warmer parts of
the earth, and only a very few occur within the limits of the United
States, and these confined to the extreme south. They are extremely
showy plants, owing to their large leaves and brilliant flowers, and
for this reason are cultivated extensively. Various species of _Canna_
(Fig. 88) are common in gardens, where they are prized for their
large, richly-colored leaves, and clusters of scarlet, orange, or
yellow flowers. The leafy stems arise from thick tubers or root
stocks, and grow rapidly to a height of two metres or more in the
larger species. The leaves, as in all the order, are very large, and
have a thick midrib with lateral veins running to the margin. The
young leaves are folded up like a trumpet. The flowers are irregular
in form, and in _Canna_ only a single stamen is found; or if more are
present, they are reduced to petal-like rudiments. The single, perfect
stamen (Fig. 88, _C_, _an._) has the filament broad and colored like
the petals, and the anther attached to one side. The pistil (_gy._) is
also petal-like. There are three circles of leaves forming the
perigone, the two outer being more or less membranaceous, and only the
three inner petal-like in texture. The ovary (_o_) is inferior, and
covered on the outside with little papillæ that afterward form short
spines on the outside of the fruit (_F_).
The seeds are large, but the embryo is very small. A section of a
nearly ripe seed shows the embryo (_em._) occupying the upper part of
the embryo sac which does not nearly fill the seed and contains no
endosperm. The bulk of the seed is derived from the tissue of the body
of the ovule, which in most seeds becomes entirely obliterated by the
growth of the embryo sac. The cells of this tissue become filled with
starch, and serve the same purpose as the endosperm of other seeds.
This tissue is called "perisperm."
Of food plants belonging to this order, the banana (_Musa_) is much
the most important. Others of more or less value are species of
arrowroot (_Maranta_) and ginger (_Zingiber_).
There are three families: I. _Musaceæ_ (banana family);
II. _Zingiberaceæ_ (ginger family); and III. _Cannaceæ_ (_Canna_,
_Maranta_).
ORDER VI.--_Gynandræ_.
By far the greater number of the plants of this order belong to the
orchis family (_Orchideæ_), the second family of the order
(_Apostasieæ_), being a small one and unrepresented in the United
States. The orchids are in some respects the most highly specialized
of all flowers, and exhibit wonderful variety in the shape and color
of the flowers, which are often of extraordinary beauty, and show
special contrivances for cross-fertilization that are without parallel
among flowering plants.
[Illustration: FIG. 89.--_Gynandræ_. _A_, inflorescence of the showy
orchis (_Orchis spectabilis_), × 1 (_Orchideæ_). _B_, a single flower,
with the upper leaves of the perianth turned back to show the column
(_x_). _sp._ the spur attached to the lower petal or lip. _o_, the
ovary, × 1. _C_, the column seen from in front. _an._ the stamen.
_gy._ the stigmatic surface, × 1. _D_, the two pollen masses attached
to a straw, which was inserted into the flower, by means of the viscid
disc (_d_): i, the masses immediately after their withdrawal; ii, iii,
the same a few minutes later, showing the change in position. _E_,
diagram of the flower; the position of the missing stamens indicated
by small circles.]
The flowers are always more or less bilaterally symmetrical
(zygomorphic). The ovary is inferior, and usually twisted so as to
turn the flower completely around. There are two sets of perigone
leaves, three in each, and these are usually much alike except the
lower (through the twisting of the ovary) of the inner set. This
petal, known as the "lip" or "labellum," is usually larger than the
others, and different in color, as well as being frequently of
peculiar shape. In many of them it is also prolonged backward in a
hollow spur (see Fig. 89, _B_). In all of the orchids except the
lady's-slippers (_Cypripedium_) (Fig. 90, _B_), only one perfect
stamen is developed, and this is united with the three styles to form
a special structure known, as the "column" or "gynostemium" (Fig. 89,
_B_, _C_). The pollen spores are usually aggregated into two or four
waxy masses ("pollinia," sing. pollinium), which usually can only be
removed by the agency of insects upon which all but a very few orchids
are absolutely dependent for the pollination of the flowers.
[Illustration: FIG. 90.--Forms of _Orchideæ_. _A_, putty-root
(_Aplectrum_), × 1. _B_, yellow lady's-slipper (_Cypripedium_), × ½.
_C_, the column of the same, × 1. _an._ one of the two perfect
stamens. _st._ sterile, petal-like stamen. _gy._. stigma. _D_,
_Arethusa_, × ½. _E_, section of the column, × 1: _an._ stamen. _gy._
stigma. _F_, the same, seen from in front. _G_, _Habenaria_, × 1. _H_,
_Calopogon_, × 1. In the last the ovary is not twisted, so that the
lip (_L_) lies on the upper side of the flower.]
In the lady-slippers there are two fertile stamens, and a third
sterile one has the form of a large triangular shield terminating the
column (Fig. 90, _C_, _st._).
The ovules of the orchids are extremely small, and are only partly
developed at the time the flower opens, the pollen tube growing very
slowly and the ovules maturing as it grows down through the tissues of
the column. The ripe seeds are excessively numerous, but so fine as to
look like dust.
The orchids are mostly small or moderate-sized plants, few of them
being more than a metre or so in height. All of our native species,
with the exception of a few from the extreme south, grow from fibrous
roots or tubers, but many tropical orchids, as is well known, are
"epiphytes"; that is, they grow upon the trunks and branches of trees.
One genus, _Vanilla_, is a twining epiphyte; the fruit of this plant
furnishes the vanilla of commerce. Aside from this plant, the
economical value of the orchids is small, although a few of them are
used medicinally, but are not specially valuable.
Of the five thousand species known, the great majority are inhabitants
of the tropics, but nevertheless there are within the United States a
number of very beautiful forms. The largest and showiest are the
lady's-slippers, of which we have six species at the north. The most
beautiful is the showy lady's-slipper (_Cypripedium spectabile_),
whose large, pink and white flowers rival in beauty many of the
choicest tropical orchids. Many of the _Habenarias_, including the
yellow and purple fringed orchids, are strikingly beautiful as are the
_Arethuseæ_ (_Arethusa_, _Pogonia_, _Calopogon_). The last of these
(Fig. 90, _H_) differs from all our other native orchids in having the
ovary untwisted so that the labellum lies on the upper side of the
flower.
A number of the orchids are saprophytic, growing in soil rich in
decaying vegetable matter, and these forms are often nearly or quite
destitute of chlorophyll, being brownish or yellowish in color, and
with rudimentary leaves. The coral roots (_Corallorhiza_), of which
there are several species, are examples of these, and another closely
related form, the putty-root (_Aplectrum_) (Fig. 90, _A_), has the
flowering stems like those of _Corallorhiza_, but there is a single,
large, plaited leaf sent up later.
ORDER VII.--_Helobiæ_.
The last order of the monocotyledons is composed of marsh or water
plants, some of which recall certain of the dicotyledons. Of the three
families, the first, _Juncagineæ_, includes a few inconspicuous plants
with grass-like or rush-like leaves, and small, greenish or yellowish
flowers (_e.g._ arrow-grass, _Triglochin_).
The second family (_Alismaceæ_) contains several large and showy
species, inhabitants of marshes. Of these the water-plantain
(_Alisma_), a plant with long-stalked, oval, ribbed leaves, and a
much-branched panicle of small, white flowers, is very common in
marshes and ditches, and the various species of arrowhead
(_Sagittaria_) are among the most characteristic of our marsh plants.
The flowers are unisexual; the female flowers are usually borne at the
base of the inflorescence, and the male flowers above. The gynœcium
(Fig. 91, _B_) consists of numerous, separate carpels attached to a
globular receptacle. The sepals are green and much smaller than the
white petals. The leaves (_F_) are broad, and, besides the thickened,
parallel veins, have numerous smaller ones connecting these.
[Illustration: FIG. 91.--Types of _Helobiæ_. _A_, inflorescence of
arrowhead (_Sagittaria_), with a single female flower, × ½
(_Alismaceæ_). _B_, section through the gynœcium, showing the numerous
single carpels, × 3. _C_, a ripe fruit, × 3. _D_, a male flower, × 1.
_E_, a single stamen, × 3. _F_, a leaf of _Sagittaria variabilis_,
× ⅙. _G_, ditch-moss (_Elodea_), with a female flower (_fl._), × ½.
(_Hydrocharideæ_). _H_, the flower, × 2. _an._ the rudimentary
stamens. _st._ the stigma. _I_, cross-section of the ovary, × 4. _J_,
male inflorescence of eel-grass (_Vallisneria_), × 1. _K_, a single
expanded male flower, × 12. _st._ the stamen. _L_, a female flower,
× 1. _gy._ the stigma.]
The last family is the _Hydrocharideæ_. They are submersed aquatics,
or a few of them with long-stalked, floating leaves. Two forms, the
ditch-moss (_Elodea_) (Fig. 91, _G_, _I_) and eel-grass
(_Vallisneria_) are very common in stagnant or slow-running water. In
both of these the plants are completely submersed, but there is a
special arrangement for bringing the flowers to the surface of the
water. Like the arrowhead, the flowers are unisexual, but borne on
different plants. The female flowers (_H_, _L_) are comparatively
large, especially in _Vallisneria_, and are borne on long stalks, by
means of which they reach the surface of the water, where they expand
and are ready for pollination. The male flowers (Fig. 91, _J_, _K_)
are extremely small and borne, many together, surrounded by a
membranous envelope, the whole inflorescence attached by a short
stalk. When the flowers are ready to open, they break away from their
attachment, and the envelope opens, allowing them to escape, and they
immediately rise to the surface where they expand and collect in great
numbers about the open female flowers. Sometimes these are so abundant
during the flowering period (late in summer) that the surface of the
water looks as if flour had been scattered over it. After pollination
is effected, the stem of the female flower coils up like a spring,
drawing the flower beneath the water where the fruit ripens.
The cells of these plants show very beautifully the circulation of the
protoplasm, the movement being very marked and continuing for a long
time under the microscope. To see this the whole leaf of _Elodea_, or
a section of that of _Vallisneria_, may be used.