481. Even the beginner in botany should have some general idea of what
cryptogamous plants are, and what are the obvious distinctions of the
principal families. Although the lower grades are difficult, and need
special books and good microscopes for their study, the higher orders,
such as Ferns, may be determined almost as readily as phanerogamous
plants.
482. Linnaeus gave to this lower grade of plants the name of
_Cryptogamia_, thereby indicating that their organs answering to stamens
and pistils, if they had any, were recondite and unknown. There is no
valid reason why this long-familiar name should not be kept up, along
with the counterpart one of _Phanerogamia_ (6), although organs
analogous to stamens and pistil, or rather to pollen and ovule, have
been discovered in all the higher and most of the lower grades of this
series of plants. So also the English synonymous name of _Flowerless
Plants_ is both good and convenient: for they have not flowers in the
proper sense. The essentials of flowers are stamens and pistils, giving
rise to seeds, and the essential of a seed is an embryo (8).
Cryptogamous or Flowerless plants are propagated by SPORES; and a spore
is not an embryo-plantlet, but mostly a single plant-cell (399).
483. =Vascular Cryptogams=, which compose the higher orders of this
series of plants, have stems and (usually) leaves, constructed upon the
general plan of ordinary plants; that is, they have wood (wood-cells and
vessels, 408) in the stem and leaves, in the latter as a frame work of
veins. But the lower grades, having only the more elementary cellular
structure, are called _Cellular Cryptogams_. Far the larger number of
the former are Ferns: wherefore that class has been called
484. =Pteridophyta, Pteridophytes= in English form, meaning
_Fern-plants_,--that is, Ferns and their relatives. They are mainly
Horsetails, Ferns, Club-Mosses, and various aquatics which have been
called _Hydropterides_, i. e. Water-Ferns.
485. =Horsetails=, _Equisetaceae_, is the name of a family which consists
only (among now-living plants) of _Equisetum_, the botanical name of
Horsetail and Scouring Rush. They have hollow stems, with partitions at
the nodes; the leaves consist only of a whorl of scales at each node,
these coalescent into a sheath: from the axils of these leaf-scales, in
many species, branches grow out, which are similar to the stem but on a
much smaller scale, close-jointed, and with the tips of the leaves more
apparent. At the apex of the stem appears the _fructification_, as it is
called for lack of a better term, in the form of a short spike or head.
This consists of a good number of stalked shields, bearing on their
inner or under face several wedge-shaped spore-cases. The spore-cases
when they ripen open down the inner side and discharge a great number
of green spores of a size large enough to be well seen by a hand-glass.
The spores are aided in their discharge and dissemination by four
club-shaped threads attached to one part of them. These are hygrometric:
when moist they are rolled up over the spore; when dry they straighten,
and exhibit lively movements, closing over the spore when breathed upon,
and unrolling promptly a moment after as they dry. (See Fig. 493-498.)
[Illustration: Fig. 493. Upper part of a stem of a Horsetail, Equisetum
sylvaticum. 494. Part of the head or spike of spore-cases, with some of
the latter taken off. 495. View (more enlarged) of under side of the
shield-shaped body, bearing a circle of spore-cases. 496. One of the
latter detached and more magnified. 497. A spore with the attached arms
moistened. 498. Same when dry, the arms extended.]
[Illustration: Fig. 499. A Tree-Fern, Dicksonia arborescens, with a
young one near its base. In front a common herbaceous Fern (Polypodium
vulgare) with its creeping stem or rootstock.]
[Illustration: Fig. 500. A section of the trunk of a Tree-Fern.]
486. =Ferns, or Filices=, a most attractive family of plants, are very
numerous and varied. In warm and equable climates some rise into
forest-trees, with habit of Palms; but most of them are perennial herbs.
The wood of a Fern-trunk is very different, however, from that of a
palm, or of any exogenous stem either. A section is represented in Fig.
500. The curved plates of wood each terminate upward in a leaf-stalk.
The subterranean trunk or stem of any strong-growing herbaceous Fern
shows a similar structure. Most Ferns are circinate in the bud; that is,
are rolled up in the manner shown in Fig. 197. Uncoiling as they grow,
they have some likeness to a crosier.
[Illustration: Fig. 501. The Walking-Fern, Camptosorus, reduced in size,
showing its fruit-dots on the veins approximated in pairs. 502. A small
piece (pinnule) of a Shield-Fern: a row of fruit-dots on each side of
the midrib, each covered by its kidney-shaped indusium. 503. A
spore-case from the latter, just bursting by the partial straightening
of the incomplete ring; well magnified. 504. Three of the spores of 509,
more magnified. 505. Schizaea pusilla, a very small and simple-leaved
Fern, drawn nearly of natural size. 506. One of the lobes of its
fruit-bearing portion, magnified, bearing two rows of spore-cases. 507.
Spore-case of the latter, detached, opening lengthwise. 508.
Adder-tongue, Ophioglossum; spore-cases in a kind of spike: _a_, a
portion of the fruiting part, about natural size; showing two rows of
the firm spore-cases, which open transversely into two valves.]
487. The fructification of Ferns is borne on the back or under side of
the leaves. The early botanists thought this such a peculiarity that
they always called a Fern-leaf a FROND, and its petiole a STIPE. Usage
continues these terms, although they are superfluous. The fruit of Ferns
consists of SPORE-CASES, technically SPORANGIA, which grow out of the
veins of the leaf. Sometimes these are distributed over the whole lower
surface of the leaf or frond, or over the whole surface when there are
no proper leaf-blades to the frond, but all is reduced to stalks.
Commonly the spore-cases occupy only detached spots or lines, each of
which is called a SORUS, or in English merely a Fruit-dot. In many Ferns
these fruit-dots are naked; in others they are produced under a
scale-like bit of membrane, called an INDUSIUM. In Maidenhair-Ferns a
little lobe of the leaf is folded back over each fruit-dot, to serve as
its shield or indusium. In the true Brake or Bracken (Pteris) the whole
edge of the fruit-bearing part of the leaf is folded back over it like a
hem.
488. The form and structure of the spore-cases can be made out with a
common hand magnifying glass. The commonest kind (shown in Fig. 503) has
a stalk formed of a row of jointed cells, and is itself composed of a
layer of thin-walled cells, but is incompletely surrounded by a border
of thicker-walled cells, forming the RING. This extends from the stalk
up one side of the spore-case, round its summit, descends on the other
side, but there gradually vanishes. In ripening and drying the shrinking
of the cells of the ring on the outer side causes it to straighten; in
doing so it tears the spore-case open on the weaker side and discharges
the minute spores that fill it, commonly with a jerk which scatters them
to the wind. Another kind of spore-case (Fig. 507) is stalkless, and has
its ring-cells forming a kind of cap at the top: at maturity it splits
from top to bottom by a regular dehiscence. A third kind is of firm
texture and opens across into two valves, like a clam-shell (Fig. 508a):
this kind makes an approach to the next family.
[Illustration: Fig. 509. A young prothallus of a Maiden-hair, moderately
enlarged, and an older one with the first fern-leaf developed from near
the notch. 510. Middle portion of the young one, much magnified, showing
below, partly among the rootlets, the _antheridia_ or fertilizing
organs, and above, near the notch, three _pistillidia_ to be
fertilized.]
489. The spores germinate on moistened ground. In a conservatory they
may be found germinating on a damp wall or on the edges of a
well-watered flower-pot. Instead of directly forming a fern-plantlet,
the spore grows first into a body which closely resembles a small
Liverwort. This is named a PROTHALLUS (Fig. 509): from some point of
this a bud appears to originate, which produces the first fern-leaf,
soon followed by a second and third, and so the stem and leaves of the
plant are set up.
[Illustration: Fig. 511. Lycopodium Carolinianum, of nearly natural
size. 512. Inside view of one of the bracts and spore-case, magnified.]
[Illustration: Fig. 513. Open 4-valved spore-case of a Selaginella, and
its four large spores (macrospores), magnified. 514. Macrospores of
another Selaginella. 515. Same separated.]
[Illustration: Fig. 516. Plant of Isoetes. 517. Base of a leaf and
contained sporocarp filled with microspores cut across, magnified. 518.
Same divided lengthwise, equally magnified; some microspores seen at the
left. 519. Section of a spore-case containing macrospores, equally
magnified; at the right three macrospores more magnified.]
490. Investigation of this prothallus under the microscope resulted in
the discovery of a wholly unsuspected kind of fertilization, taking
place at this germinating stage of the plant. On the under side of the
prothallus two kinds of organs appear (Fig. 510). One may be likened to
an open and depressed ovule, with a single cell at bottom answering to
nucleus; the other, to an anther; but instead of pollen, it discharges
corkscrew-shaped microscopic filaments, which bear some cilia of extreme
tenuity, by the rapid vibration of which the filaments move freely over
a wet surface. These filaments travel over the surface of the
prothallus, and even to other prothalli (for there are natural hybrid
Ferns), reach and enter the ovule-like cavities, and fertilize the
cell. This thereupon sets up a growth, forms a vegetable bud, and so
develops the new plant.
491. An essentially similar process of fertilization has been discovered
in the preceding and the following families of Pteridophytes; but it is
mostly subterranean and very difficult to observe.
492. =Club-Mosses or Lycopodiums.= Some of the common kinds, called
Ground Pine, are familiar, being largely used for Christmas wreaths and
other decoration. They are low evergreens, some creeping, all with
considerable wood in their stems: this thickly beset with small leaves.
In the axils of some of these leaves, or more commonly, in the axils of
peculiar leaves changed into bracts (as in Fig. 511, 512) spore-cases
appear, as roundish or kidney-shaped bodies, of firm texture, opening
round the top into two valves, and discharging a great quantity of a
very fine yellow powder, the spores.
493. The Selaginellas have been separated from Lycopodium, which they
much resemble, because they produce two kinds of spores, in separate
spore-cases. One kind (MICROSPORES) is just that of Lycopodium; the
other consists of only four large spores (MACROSPORES), in a spore-case
which usually breaks in pieces at maturity (Fig. 513-515).
494. =The Quillworts, Isoetes= (Fig. 516-519), are very unlike Club
Mosses in aspect, but have been associated with them. They look more
like Rushes, and live in water, or partly out of it. A very short stem,
like a corm, bears a cluster of roots underneath; above it is covered by
the broad bases of a cluster of awl-shaped or thread-shaped leaves. The
spore-cases are immersed in the bases of the leaves. The outer
leaf-bases contain numerous macrospores; the inner are filled with
innumerable microspores.
[Illustration: Fig. 520. Plant of Marsilia quadrifoliata, reduced in
size; at the right a pair of sporocarps of about natural size.]
495. =The Pillworts= (_Marsilia_ and _Pilularia_) are low aquatics,
which bear globular or pill-shaped fruit (SPOROCARPS) on the lower part
of their leaf-stalks or on their slender creeping stems. The leaves of
the commoner species of Marsilia might be taken for four-leaved Clover.
(See Fig. 520.) The sporocarps are usually raised on a short stalk.
Within they are divided lengthwise by a partition, and then crosswise by
several partitions. These partitions bear numerous delicate sacs or
spore-cases of two kinds, intermixed. The larger ones contain each a
large spore, or macrospore; the smaller contain numerous microspores,
immersed in mucilage. At maturity the fruit bursts or splits open at
top, and the two kinds of spores are discharged. The large ones in
germination produce a small prothallus; upon which the contents of the
microspores act in the same way as in Ferns, and with a similar result.
496. =Azolla= is a little floating plant, looking like a small Liverwort
or Moss. Its branches are covered with minute and scale-shaped leaves.
On the under side of the branches are found egg-shaped thin-walled
sporocarps of two kinds. The small ones open across and discharge
microspores; the larger burst irregularly, and bring to view globose
spore-cases, attached to the bottom of the sporocarp by a slender stalk.
These delicate spore-cases burst and set free about four macrospores,
which are fertilized at germination, in the manner of the Pillworts and
Quillworts. (See Fig. 521-526.)
[Illustration: Fig. 521. Small plant of Azolla Caroliniana. 522. Portion
magnified, showing the two kinds of sporocarp; the small ones contain
microspores. 523 represents one more magnified. 524. The larger
sporocarp more magnified. 525. Same more magnified and burst open,
showing stalked spore-cases. 526. Two of the latter highly magnified;
one of them bursting shows four contained macrospores; between the two,
three of these spores highly magnified.]
497. =Cellular Cryptogams= (483) are so called because composed, even in
their higher forms, of cellular tissue only, without proper wood-cells
or vessels. Many of the lower kinds are mere plates, or ribbons, or
simple rows of cells, or even single cells. But their highest orders
follow the plan of Ferns and phanerogamous plants in having stem and
leaves for their upward growth, and commonly roots, or at least
rootlets, to attach them to the soil, or to trunks, or to other bodies
on which they grow. Plants of this grade are chiefly Mosses. So as a
whole they take the name of
498. =Bryophyta, Bryophytes= in English form, Bryum being the Greek name
of a Moss. These plants are of two principal kinds: true Mosses
(_Musci_, which is their Latin name in the plural); and Hepatic Mosses,
or Liverworts (_Hepaticae_).
[Illustration: Fig. 527. Single plant of Physcomitrium pyriforme,
magnified. 528. Top of a leaf, cut across; it consists of a single layer
of cells.]
499. =Mosses or Musci.= The pale Peat-mosses (species of Sphagnum, the
principal component of sphagnous bogs) and the strong-growing Hair-cap
Moss (Polytrichum) are among the larger and commoner representatives of
this numerous family; while Fountain Moss (Fontinalis) in running water
sometimes attains the length of a yard or more. On the other hand, some
are barely individually distinguishable to the naked eye. Fig. 527
represents a common little Moss, enlarged to about twelve times its
natural size; and by its side is part of a leaf, much magnified, showing
that it is composed of cellular tissue (parenchyma-cells) only. The
leaves of Mosses are always simple, distinct, and sessile on the stem.
The fructification is an urn-shaped spore-case, in this as in most cases
raised on a slender stalk. The spore-case loosely bears on its summit a
thin and pointed cap, like a candle-extinguisher, called a _Calyptra_.
Detaching this, it is found that the spore-case is like a pyxis (376),
that is, the top at maturity comes off as a lid (_Operculum_); and that
the interior is filled with a green powder, the spores, which are
discharged through the open mouth. In most Mosses there is a fringe of
one or two rows of teeth or membrane around this mouth or orifice, the
_Peristome_. When moist the peristome closes hygrometrically over the
orifice more or less; when drier the teeth or processes commonly bend
outward or recurve; and then the spores more readily escape. In Hair-cap
Moss a membrane is stretched quite across the mouth, like a drum-head,
retaining the spores until this wears away. See Figures 527-541 for
details.
500. Fertilization in Mosses is by the analogues of stamens and pistils,
which are hidden in the axils of leaves, or in the cluster of leaves at
the end of the stem. The analogue of the anther (_Antheridium_) is a
cellular sac, which in bursting discharges innumerable delicate cells
floating in a mucilaginous liquid; each of these bursts and sets free a
vibratile self-moving thread. These threads, one or more, reach the
orifice of the pistil-shaped body, the _Pistillidium_, and act upon a
particular cell at its base within. This cell in its growth develops
into the spore-case and its stalk (when there is any), carrying on its
summit the wall of the pistillidium, which becomes the calyptra.
[Illustration: Fig. 529. Mnium cuspidatum, smaller than nature. 530. Its
calyptra, detached, enlarged. 531. Its spore-case, with top of stalk,
magnified, the lid (532) being detached, the outer peristome appears.
533. Part of a cellular ring (_annulus_) which was under the lid,
outside of the peristome, more magnified. 534. Some of the outer and of
the inner peristome (consisting of jointed teeth) much magnified. 535.
Antheridia and a pistillidium (the so-called flower) at end of a stem of
same plant, the leaves torn away ([Symbol for Male], antheridia, [Symbol
for Female], pistillidium), magnified. 536. A bursting antheridium, and
some of the accompanying jointed threads, highly magnified. 537. Summit
of an open spore-case of a Moss, which has a peristome of 16 pairs of
teeth. 538. The double peristome of a Hypnum. 539-541. Spore-case,
detached calyptra, and top of more enlarged spore-case and detached lid,
of Physcomitrium pyriforme (Fig. 527): orifice shows that there is no
peristome.]
501. =Liverworts or Hepatic Mosses= (_Hepaticae_) in some kinds resemble
true Mosses, having distinct stem and leaves, although their leaves
occasionally run together; while in others there is no distinction of
stem and leaf, but the whole plant is a leaf-like body, which produces
rootlets on the lower face and its fructification on the upper. Those of
the moss-like kind (sometimes called Scale-Mosses) have their tender
spore-cases splitting into four valves; and with their spores are
intermixed some slender spiral and very hygrometric threads (called
_Elaters_) which are thought to aid in the dispersion of the spores.
(Fig. 542-544.)
[Illustration: Fig. 542. Fructification of a Jungermannia, magnified;
its cellular spore-stalk, surrounded at base by some of the leaves, at
summit the 4-valved spore-case opening, discharging spores and elaters.
543. Two elaters and some spores from the same, highly magnified.]
[Illustration: Fig. 544. One of the frondose Liverworts, Steetzia,
otherwise like a Jungermannia; the spore-case not yet protruded from its
sheath.]
502. Marchantia, the commonest and largest of the true Liverworts, forms
large green plates or fronds on damp and shady ground, and sends up from
some part of the upper face a stout stalk, ending in a several-lobed
umbrella-shaped body, under the lobes of which hang several thin-walled
spore-cases, which burst open and discharge spores and elaters. Riccia
natans (Fig. 545) consists of wedge-shaped or heart-shaped fronds, which
float free in pools of still water. The under face bears copious
rootlets; in the substance of the upper face are the spore-cases, their
pointed tips merely projecting: there they burst open, and discharge
their spores. These are comparatively few and large, and are in fours;
so they are very like the macrospores of Pillworts or Quillworts.
503. =Thallophyta, or Thallophytes= in English form. This is the name
for the lower class of Cellular Cryptogams,--plants in which there is no
marked distinction into root, stem, and leaves. Roots in any proper
sense they never have, as organs for absorbing, although some of the
larger Seaweeds (such as the Sea Colander, Fig. 553) have them as
holdfasts. Instead of axis and foliage, there is a stratum of frond, in
such plants commonly called a THALLUS (by a strained use of a Greek and
Latin word which means a green shoot or bough), which may have any kind
of form, leaf-like, stem-like, branchy, extended to a flat plate, or
gathered into a sphere, or drawn out into threads, or reduced to a
single row of cells, or even reduced to single cells. Indeed,
Thallophytes are so multifarious, so numerous in kinds, so protean in
their stages and transformations, so recondite in their fructification,
and many so microscopic in size, either of the plant itself or its
essential organs, that they have to be elaborately described in separate
books and made subjects of special study.
[Illustration: Fig. 545, 546. Two plants of Riccia natans, about natural
size. 547. Magnified section of a part of the frond, showing two
immersed spore-cases, and one emptied space. 548. Magnified section of a
spore-case with some spores. 549. Magnified spore-case torn out, and
spores; one figure of the spores united; the other of the four
separated.]
504. Nevertheless, it may be well to try to give some general idea of
what Algae and Lichens and Fungi are. Linnaeus had them all under the
orders of Algae and Fungi. Afterwards the Lichens were separated; but of
late it has been made most probable that a Lichen consists of an Alga
and a Fungus conjoined. At least it must be so in some of the ambiguous
forms. Botanists are in the way of bringing out new classifications of
the Thallophytes, as they come to understand their structure and
relations better. Here, it need only be said that
505. Lichens live in the air, that is, on the ground, or on rocks,
trunks, walls, and the like, and grow when moistened by rains. They
assimilate air, water, and some earthy matter, just as do ordinary
plants. Algae, or Seaweeds, live in water, and live the same kind of life
as do ordinary plants. Fungi, whatever medium they inhabit, live as
animals do, upon organic matter,--upon what other plants have
assimilated, or upon the products of their decay. True as these general
distinctions are, it is no less true that these orders run together in
their lowest forms; and that Algae and Fungi may be traced down into
forms so low and simple that no clear line can be drawn between them;
and even into forms of which it is uncertain whether they should be
called plants or animals. It is as well to say that they are not high
enough in rank to be distinctively either the one or the other. On the
other hand there is a peculiar group of plants, which in simplicity of
composition resemble the simpler Algae, while in fructification and in
the arrangements of their simple cells into stem and branches they seem
to be of a higher order, viz.:--
[Illustration: Fig. 550. Branch of a Chara, about natural size. 551. A
fruiting portion, magnified, showing the structure; a sporocarp, and an
antheridium. 552. Outlines of a portion of the stem in section, showing
the central cell and the outer or cortical cells.]
506. =Characeae.= These are aquatic herbs, of considerable size,
abounding in ponds. The simpler kinds (Nitella) have the stem formed of
a single row of tubular cells, and at the nodes, or junction of the
cells, a whorl of similar branches. Chara (Fig. 550-552) is the same,
except that the cells which make up the stem and the principal branches
are strengthened by a coating of many smaller tubular cells, applied to
the surface of the main or central cell. The fructification consists of
a globular sporocarp of considerable size, which is spirally enwrapped
by tubular cells twisted around it: by the side of this is a smaller and
globular antheridium. The latter breaks up into eight shield-shaped
pieces, with an internal stalk, and bearing long and ribbon shaped
filaments, which consist of a row of delicate cells, each of which
discharges a free-moving microscopic thread (the analogue of the pollen
or pollen-tube), nearly in the manner of Ferns and Mosses. One of these
threads reaches and fertilizes a cell at the apex of the nucleus or
solid body of the sporocarp. This subsequently germinates and forms a
new individual.
507. =Algae or Seaweeds.= The proper Seaweeds may be studied by the aid
of Professor Farlow's "Marine Algae of New England;" the fresh-water
species, by Prof. H. C. Woods's "Fresh-water Algae of North America," a
larger and less accessible volume. A few common forms are here very
briefly mentioned and illustrated, to give an idea of the family. But
they are of almost endless diversity.
[Illustration: Fig. 553. Agarum Turneri, Sea Colander (so called from
the perforations with which the frond, as it grows, becomes riddled);
very much reduced in size.]
[Illustration: Fig. 554. Upper end of a Rockweed, Fucus vesiculosus,
reduced half or more, _b_, the fructification.]
508. The common Rockweed (Fucus vesiculosus, Fig. 554, abounding between
high and low water mark on the coast), the rarer Sea Colander (Agarum
Turneri, Fig. 553), and Laminaria, of which the larger forms are called
Devil's Aprons, are good representatives of the olive green or brownish
Seaweeds. They are attached either by a disk-like base or by root-like
holdfasts to the rocks or stones on which they grow.
[Illustration: Fig. 555. Magnified section through a fertile conceptacle
of Rockweed, showing the large spores in the midst of threads of cells.
556. Similar section of a sterile conceptacle, containing slender
antheridia. From Farlow's "Marine Algae of New England."]
509. The hollow and inflated places in the Fucus vesiculosus or Rockweed
(Fig. 554) are air-bladders for buoyancy. The fructification forms in
the substance of the tips of the frond: the rough dots mark the places
where the conceptacles open. The spores and the fertilizing cells are in
different plants. Sections of the two kinds of conceptacles are given in
Fig. 555 and 556. The contents of the conceptacles are discharged
through a small orifice which in each figure is at the margin of the
page. The large spores are formed eight together in a mother-cell. The
minute motile filaments of the antheridia fertilize the large spores
after injection into the water: and then the latter promptly acquire a
cell-wall and germinate.
510. The Florideae or Rose-red series of marine Algae (which, however, are
sometimes green or brownish) are the most attractive to amateurs. The
delicate Porphyra or Laver is in some countries eaten as a delicacy, and
the cartilaginous Chondrus crispus has been largely used for jelly.
Besides their conceptacles, which contain true spores (Fig. 560), they
mostly have a fructification in _Tetraspores_, that is, of spores
originating in fours (Fig. 559).
[Illustration: Fig. 557. Small plant of Chondrus crispus, or Carrageen
Moss, reduced in size, in fruit; the spots represent the fructification,
consisting of numerous tetraspores in bunches in the substance of the
plant. 558. Section through the thickness of one of the lobes,
magnified, passing through two of the imbedded fruit-clusters. 559. Two
of its tetraspores (spores in fours), highly magnified.]
[Illustration: Fig. 560. Section through a conceptacle of Delesseria
Leprieurei, much magnified, showing the spores, which are single
specialized cells, two or three in a row.]
[Illustration: Fig. 561. A piece of the rose-red Delesseria Leprieurei,
double natural size. 562. A piece cut out and much magnified, showing
that it is composed of a layer of cells. 563. A few of the cells more
highly magnified: the cells are gelatinous and thick-walled.]
511. The Grass-green Algae sometimes form broad membranous fronds, such
as those of the common Ulva of the sea-shore, but most of them form mere
threads, either simple or branched. To this division belong almost all
the Fresh-water Algae, such as those which constitute the silky threads
or green slime of running streams or standing pools, and which were all
called Confervas before their immense diversity was known. Some are
formed of a single row of cells, developed each from the end of another.
Others branch, the top of one cell producing more than one new one (Fig.
564). Others, of a kind which is very common in fresh water, simple
threads made of a line of cells, have the chlorophyll and protoplasm of
each cell arranged in spiral lines or bands. They form spores in a
peculiar way, which gives to this family the designation of conjugating
Algae.
[Illustration: Fig. 564. The growing end of a branching Conferva
(Cladophora glomerata), much magnified; showing how, by a kind of
budding growth, a new cell is formed by a cross partition separating the
newer tip from the older part below; also, how the branches arise.]
[Illustration: Fig. 565. Two magnified individuals of a Spirogyra,
forming spores by conjugation; a completed spore at base: above,
successive stages of the conjugation are represented.]
512. At a certain time two parallel threads approach each other more
closely; contiguous parts of a cell of each thread bulge or grow out,
and unite when they meet; the cell-wall partitions between them are
absorbed so as to open a free communication; the spiral band of green
matter in both cells breaks up; the whole of that of one cell passes
over into the other; and of the united contents a large green spore is
formed. Soon the old cells decay, and the spore set free is ready to
germinate. Fig. 565 represents several stages of the conjugating
process, which, however, would never be found all together like this in
one pair of threads.
[Illustration: Fig. 566. Closterium acutum, a common Desmid, moderately
magnified. It is a single firm-walled cell, filled with green
protoplasmic matter.]
[Illustration: Fig. 567. More magnified view of three stages of the
conjugation of a pair of the same.]
513. Desmids and Diatomes, which are microscopic one-celled plants of
the same class, conjugate in the same way, as is shown in a Closterium
by Fig. 566, 567. Here the whole living contents of two individuals are
incorporated into one spore, for a fresh start. A reproduction which
costs the life of two individuals to make a single new one would be
fatal to the species if there were not a provision for multiplication by
the prompt division of the new-formed individual into two, and these
again into two, and so on in geometrical ratio. And the costly process
would be meaningless if there were not some real advantage in such a
fresh start, that is, in sexes.
[Illustration: Fig. 568. Early stage of a species of Botrydium, a
globose cell. 569, 570. Stages of growth. 571. Full-grown plant,
extended and ramified below in a root-like way. 572. A Vaucheria; single
cell grown on into a much-branched thread; the end of some branches
enlarging, and the green contents in one (_a_) there condensed into a
spore. 573. More magnified view of _a_, and the mature spore escaping.
574. Bryopsis plumosa; apex of a stem with its branchlets; all the
extension of one cell. Variously magnified.]
514. There are other Algae of the grass-green series which consist of
single cells, but which by continued growth form plants of considerable
size. Three kinds of these are represented in Fig. 568-574.
515. =Lichens=, Latin _Lichenes_, are to be studied in the works of the
late Professor Tuckerman, but a popular exposition is greatly needed.
The subjoined illustrations (Fig. 575-580) may simply indicate what some
of the commoner forms are like. The cup, or shield-shaped spot, or knob,
which bears the fructification is named the _Apothecium_. This is mainly
composed of slender sacs (_Asci_), having thread-shaped cells
intermixed; and each ascus contains few or several spores, which are
commonly double or treble. Most Lichens are flat expansions of grayish
hue; some of them foliaceous in texture, but never of bright green
color; more are crustaceous; some are wholly pulverulent and nearly
formless. But in several the vegetation lengthens into an axis (as in
Fig. 580), or imitates stem and branches or threads, as in the
Reindeer-Moss on the ground in our northern woods, and the Usnea hanging
from the boughs of old trees overhead.
[Illustration: Fig. 575. A stone on which various Lichens are growing,
such as (passing from left to right) a Parmelia, a Sticta, and on the
right, Lecidia geographica, so called from its patches resembling the
outline of islands or continents as depicted upon maps. 576. Piece of
thallus of Parmelia conspersa, with section through an apothecium. 577.
Section of a smaller apothecium, enlarged. 578. Two asci of same, and
contained spores, and accompanying filaments; more magnified. 579. Piece
of thallus of a Sticta, with section, showing the immersed apothecia;
the small openings of these dot the surface. 580. Cladonia coccinea; the
fructification is in the scarlet knobs, which surround the cups.]
516. =Fungi.= For this immense and greatly diversified class, it must
here suffice to indicate the parts of a Mushroom, a Sphaeria, and of one
or two common Moulds. The true vegetation of common Fungi consists of
slender cells which form what is called a _Mycelium_. These filamentous
cells lengthen and branch, growing by the absorption through their
whole surface of the decaying, or organizable, or living matter which
they feed upon. In a Mushroom (Agaricus), a knobby mass is at length
formed, which develops into a stout stalk (_Stipe_), bearing the cap
(_Pileus_): the under side of the cap is covered by the _Hymenium_, in
this genus consisting of radiating plates, the gills or _Lamellae_; and
these bear the powdery spores in immense numbers. Under the microscope,
the gills are found to be studded with projecting cells, each of which,
at the top, produces four stalked spores. These form the powder which
collects on a sheet of paper upon which a mature Mushroom is allowed to
rest for a day or two. (Fig. 581-586.)
517. The esculent Morel, also Sphaeria (Fig. 585, 586), and many other
Fungi bear their spores in sacs (asci) exactly in the manner of Lichens
(515).
[Illustration: Fig. 581. Agaricus campestris, the common edible
Mushroom. 582. Section of cap and stalk. 583. Minute portion of a
section of a gill, showing some spore-bearing cells, much magnified.
584. One of these, with its four spores, more magnified.]
[Illustration: Fig. 585. Sphaeria rosella. 586. Two of the asci and
contained double spores, quite like those of a Lichen; much magnified.]
518. Of the Moulds, one of the commoner is the Bread-Mould (Fig. 587).
In fruiting it sends up a slender stalk, which bears a globular sac;
this bursts at maturity and discharges innumerable spores. The blue
Cheese-Mould (Fig. 588) bears a cluster of branches at top, each of
which is a row of naked spores, like a string of beads, all breaking
apart at maturity. Botrytis (Fig. 589), the fruiting stalk of which
branches, and each branch is tipped with a spore, is one of the many
moulds which live and feed upon the juices of other plants or of
animals, and are often very destructive. The extremely numerous kinds of
smut, rust, mildew, the ferments, bacteria, and the like, many of them
very destructive to other vegetable and to animal life, are also low
forms of the class of Fungi.[1]
[Illustration: Fig. 587. Ascophora, the Bread-Mould. 588. Aspergillus
glaucus, the mould of cheese, but common on mouldy vegetables. 589. A
species of Botrytis. All magnified.]
FOOTNOTES:
[1] The "Introduction to Cryptogamous Botany," or third volume of "The
Botanical Text Book," now in preparation by the author's colleague,
Professor Farlow, will be the proper guide in the study of the
Flowerless Plants, especially of the Algae and Fungi.