190

LICHENS-CHARAS.

somewhat horn-shaped body of a dark purple color, is formed.

After remaining dormant during the winter, the Ergot or Sclerotium produces spores in the following manner: Stalked receptacles grow up from the tissue of the Ergot, in which are developed a number of perithecia. These perithecia are somewhat flask-shaped cavities, which are filled with asci, the latter containing long slender spores, termed ascospores, which, by germinating on the Rye or allied Grasses, can again give rise to the sphacelia.

2. Lichenes or Lichens.-From the more recent researches which have been made on this order of plants, it appears to be most probable that Lichens are in reality Ascomycetous Fungi, parasitic upon Algæ. This question can not as yet be considered as absolutely settled, and Lichens present so many characteristics peculiar to themselves that we have no space here to describe them and their modes of reproduction. According to the view that Lichens are species of Fungi, the chlorophyl-containing cells or gonidia found within the substance of their thallus, and which used formerly to be regarded as special asexual reproductive organs, are in reality Alge upon which the Fungus is parasitic. Thus the thallus of a Lichen is a compound structure, consisting of two elements, the fungal and the algal.

3. Characeæ or Charas.-By many botanists the Charas are classed among the Algæ, but, as they present in their structure and mode of reproduction many points of difference, we have placed them in a separate group immediately preceding the latter order.

The reproductive organs are of two kinds, both of which grow at the base of the branches, and either on the same or on different branches of the same plant, or on different plants. These organs are called, respectively, globules and nucules. The globule is regarded as an antheridium, and the nucule as a pistillidium.

ALGE OR SEA-WEEDS.

191

4. Algæ or Sea-weeds.-This order of plants, like the Fungi, comprises a very large number of species, which vary exceedingly in form, size, color, and other peculiarities. They are all either inhabitants of water, salt or fresh, or live on moist surfaces, and may be microscopic plants, or growths of enormous size. Adopting no special classification of the Algae, we will simply describe the processes of reproduction occurring in spirogyra, an alga in which the process of reproduction known as conjugation very commonly takes place. It may be found in great quantities in most ponds toward the end of summer, and is one of the prettiest objects which can be examined under the microscope. Seen with the naked eye, it consists of a mass of long, very slender, green threads or filaments, which float in the water where they are growing. Examined with the microscope, each filament is seen to be more or less cylindrical, and composed of a great number of similar cells placed end to end (Fig. 230). The chlorophyl is arranged in the parietal layer of protoplasm of the cell in a definite spiral manner, the name of some of the species being determined by the number of such spirals in a single cell. Each cell is capable of growth and division, and by this means the bulk of the entire plant is increased.

FIG. 230.-Two filaments of Spirogyra about to conjugate; each cell is seen to contain chlorophyl arranged in spiral bands with grains of starch, oil globules, and a central nucleus, surrounded by protoplasmic threads which extend to the cell-wall. a, b, c. Lateral protrusions of the cell-walls of adjoining cells.

When conjugation is about to take place, two filaments approach each other, and from the sides of contiguous cells (Fig. 230, a, b, c), protrusions of the wall occur which meet in the center. The walls then intervening between the cavities of the two conjugat

192

SPIROGYRA FUCUS.

ing cells next become absorbed (Fig. 231, A, a), and the protoplasm of one cell separates itself from its cell-wall,

gating. a. Formation of a zygospore. b. a zygospore (Figs. 230, A, Formed zygospore. B. A filament in which are young zygospores, c, and which are seen to contain drops of oil. (After Sachs.)

b, and B, c). Later on its

color changes from green

to that of a deep red, and after remaining dormant during the winter the zygospore germinates at the beginning of spring, and so gives rise to a new Spirogyra plant.

Fucus.-This genus includes numerous species, which form the various plants commonly known as Sea-weeds. The thallus (Fig. 5) is usually long, very much branched, and of a greenish-brown color. In structure, it is made up at the surface of closely-packed small cells, but toward the interior the cells are more elongated, and joined end to end, so as to form filaments which are interwoven among one another. The walls of the constituent cells are peculiar in consisting of two parts, an inner firm layer, and an outer one, which is generally more or less swollen by imbibition of water.

Reproduction is effected by a sexual process, which takes place in the following way: Numerous little cavities, known as conceptacles, appear sunk in the surface of large swollen receptacles (Fig. 5, t, t), on the ends of the longer forked branches of the Fucus, and in these are contained the antheridia or oogonia, or both of these organs, together with abortive filaments or paraphyses. Some species, as

FUCUS VESICULOSUS.

193

Fucus platycarpus, are monoecious, i. e., contain both antheridia and oogonia in the same conceptacle; but in others, as Fucus vesiculosus, either only antheridia or oogonia conceptacles are produced on the same plant; such species, therefore, are diœcious.

[In the "Descriptive Botany," which is introductory to this volume, there are no exercises upon Flowerless plants. Their study is mostly pursued with the microscope, and hence their classification can not be achieved in our ordinary schools. But in "Structural and Physiological Botany" it is needful that the pupil should perceive the essential unity of plan in the two leading divisions of the vegetable kingdom. The foregoing pages were designed, therefore, to give such a general account of the reproductive process in Cryptogamous plants as would make this fact apparent. In selecting from the Author's numerous examples of modes of fructification by spores, we have given prominence to Ferns among Cormophytes, and Mushrooms among Thallophytes, because these plants are widely distributed, and their parts can be easily observed.

Gather as many kinds of Ferns as you can, and look for the little brown patches on the surface of the Fronds. With your magnifying glass you may see little bodies escaping from beneath the indusium, each of which is a spore-case, as shown in Fig. 211. Observe the underground stems of the ferns of our climate.

The Common Mushroom, found everywhere growing upon decaying matter, illustrates the stemless character of the vegetative portion of Thallophytes. The tangled mass of filaments called the mycelium, concealed in the rich mold, answers to the root, stem, and leaves of the higher plants. The portion above ground," the toadstool," represented in Fig. 227, exhibits all the parts shown in the Figure; and you will also find it surrounded by the young fruit in all stages of growth, as shown in Fig. 228.]

PART II.

PHYSIOLOGICAL BOTANY.

PHYSIOLOGY is that department of botany which considers plants in a living state, and traces the laws which regulate their life, growth, and reproduction. The various processes going on in the plant are called its functions.

CHAPTER I.

SPECIAL PHYSIOLOGY OF THE ELEMENTARY
STRUCTURES AND OF THE ORGANS
OF NUTRITION.

SECTION 1. PHYSIOLOGY OF THE ELEMENTARY STRUCT

URES.

1. Functions of Parenchymatous Cells.—As the simplest forms of vegetable life, such as the Red Snow Plant (Protococcus nivalis) (Fig. 1), consist of a single cell of a parenchymatous nature, such a cell is necessarily capable of performing all the actions appertaining to plant life. Parenchyma also constitutes the whole structure of Thallophytes, as well as the soft portions of all plants above them; hence the physiology of parenchymatous cells is of the first importance. The more important vital actions of these cells are, 1. Formation of new cells; 2. Absorption and transmission of fluids; 3. Movements in their contents; and, 4. Elaboration of their fluid contents, and production of the various organic compounds of plants.

(1) Formation of Cells (Cytogenesis).-All plants, as we have seen (page 5), in their earliest conditions, are