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12. Hypha, Willd.; the filamentous, fleshy, watery thallus of

Byssaceæ. 13. Sporangia ; any kind of case not obviously a joint of the

plant, within which spores are generated. 14. Coniocysta ; tubercle-like closed apothecia, containing a

mass of sporules; the same as sporangium.

9. Fungacee. The structure of these plants is yet more simple than that of Algaceæ, consisting of little besides cellular tissue, among which spores are generated. Some, of the lowest degree of developement, are composed only of a few cellules, of which one is larger than the rest, and contains the spores; others are more highly compounded, consisting of myriads of cellules, with the sporules lying in cases, or asci.

Sexes have been generally denied to Fungaceæ: but M. Leveillé has shown that, in the Agaric and some other high forms of the order, there are two sorts of organs; the one prominent cells containing a highly attenuated form of matter, and the other undoubtedly spores; and that these two kinds of organs are intermingled with each other. There is, however, as yet, no proof that the prominent cells are male organs.

Corda has shown that spiral-threaded cells, analogous to elaters, exist in the genus Trichia.

It is exclusively among these plants that we meet with cases of parasitism upon living animal bodies. The silkworm, and hymenopterous insects, are destroyed by the action of certain species of Botrytis in the one case, and Sphæria in the other, which attack them while alive.

Notwithstanding the extreme simplicity of these plants, writers upon Fungi have contrived to multiply the terms relating to them in a remarkable manner. The following are all with which I am acquainted :1. The Pileus, or Cap, is the uppermost part of the plant of

an Agaricus, and resembles an umbrella in form. 2. The Stipes, is the stalk that supports the pileus. 3. The Volva, or Wrapper, is the involucrum-like base of the stipes of Agaricus. It originally was a bag enveloping the whole plant, and was left at the foot of the stipes

when the plant elongated and burst through it. 4. The Velum, or Veil, is a horizontal membrane, connecting

the margin of the pileus with the stipes : when it is adnate with the surface of the pileus, it is a velum universale ; when it extends only from the margin of the

pileus to the stipes, it is a velum partiale. 5. The Annulus, is that part of the veil which remains next

the stipes, which it surrounds like a loose collar. 6. Cortina, is a name given to a portion of the velum which

adheres to the margin of the pileus in fragments. 7. The Hymenium, is the part in which the sporules imme

diately lie; in Agaricus, it consists of parallel plates, called lamellæ, or gills. These are adnate with the stipes, when the end next it coheres with it: when they are adnate, and at the same time do not terminate abruptly at the stipes, but are carried down it more or less, they are decurrent ; if they do not adhere to the stipes, they

are said to be free. 8. Stroma, is a fleshy body to which flocci are attached; as

in Isaria and Cephalotrichum. 9. Flocci, are woolly filaments found mixed with sporules in

the inside of many Gastromyci. The same name is also

applied to the external filaments of Byssaceæ. 10. Orbiculus, is a round flat hymenium contained within the

peridium of some fungi; as Nidularia. W. 11. Nucleus, is the central part of a perithecium. 12. Sporangium, is the external case of Lycoperdon and its

allies. 13. Sporangiola, are cases containing sporidia. 14. Perithecium, is a term used to express the part which

contains the reproductive organs of Sphæria and its co

ordinates. 15. Peridium, is also a kind of covering of sporidia; peridio

lum is its diminutive. 16. Ostiolum, is the orifice of the perithecium of Sphæria. 17. Spherula, is a globose peridium, with a central opening through which sporidia are emitted, mixed with a gela

tinous pulp. 18. Capillitium, is a kind of purse or net, in which the sporules

of some Fungi are retained; as in Trichia. W. 19. Trichidium, or Pecten, is a tender, simple, or sometimes

branched hair, which supports the sporules of some

Fungi; as Geastrum. W. 20. Asci, are the tubes in which the sporidia are placed;

ascelli or thecæ are the same thing. 21. Sporidia, are the immediate covering of sporules. Spo

ridiola, are sporules. 22. Thallus, or Thalamus, is the bed of fibres from which

many Fungi arise. 23. Mycelia, are the rudiments of Fungi, or the matter from

which Fungi are produced. 24. Cystidia, are the projecting cells, or supposed male organs,

of Agarics, &c. 25. Basidia, are the cells on the apex of which the spores of

such plants are formed.

277

BOOK II.

PHYSIOLOGY; OR, PLANTS CONSIDERED IN A STATE

OF ACTION.

GENERAL CONSIDERATIONS.

We have thus far considered plants as inert bodies, having certain modifications of structure, and formed upon a plan, the simplicity and uniformity of which is among the most beautiful proofs of the boundless power and skill of the Deity.

Our next business is to enquire into the nature of their vital actions, and to consider those phenomena in which the analogy that undoubtedly exists between plants and animals is most striking; in a word, to make ourselves acquainted with what is known of the laws of vegetable life.

In explaining these things, it is not my purpose to notice all the different speculations that ingenious men have from time to time brought forward: for this would be incompatible with the plan of my work, and would be far more curious than useful. On the contrary, I propose, in the first place, to give a summary exposition of the principal phenomena of vegetation, and then to support the statement by a detailed account of the more important proofs of all disputed points.

In this I have been materially assisted by the Physiologie Végétale of De Candolle, a work of which it is difficult to speak in terms of sufficient eulogy, but which I feel justified in describing as the most important production on the subject of Vegetable Physiology, since the appearance of the Physique des Arbres of Duhamel.

I. If we place a seed (that of an apple, for instance) in earth at the temperature of 32° Fahr., it will remain inactive till it finally decays. But if it is placed in moist earth above the temperature of 32°, and screened from the action of light, its integument gradually imbibes moisture and swells; the tissue is softened, and acquires the capability of stretching; the water is decomposed, and a part of its oxygen, combining with the carbon of the seed, forms carbonic acid, which is expelled; nutritious food for the young parts is prepared by the conversion of starch into sugar; and the vital action of the embryo commences. It lengthens downwards by the radicle, and upwards by the cotyledons; the former penetrating the soil, the latter elevating themselves above it, acquiring a green colour by the decomposition of the carbonic acid they absorb from the earth and atmosphere, and unfolding in the form of two opposite roundish leaves. This is the first stage of vegetation: the young plant consists of little more than cellular tissue; only an imperfect developement of vascular and fibrous tissue being discoverable, in the form of a sort of cylinder, lying just in the centre. The part within the cylinder, at its upper end, is now the pith, without it the bark; while the cylinder itself is the preparation for the medullary sheath, and consists of vertical tubes passing through and separated by cellular tissue.

The young root is now lengthening at its point, and absorbing from the earth its nutriment, which passes up to the summit of the plant by the cellular substance, and is, in part, impelled into the cotyledons, where it is aërated and evaporated, but chiefly urged upwards against the growing point or plumule.

II. Forced onwards by the current of sap, which is continually impelled upwards from the root, the plumule next ascends in the form of a little twig, at the same time sending downwards, in the centre of the radicle, the earliest portion of wood that is deposited, and compelling the root to emit little ramifications; and simultaneously the process of lignification is going on in all the tissue, by the deposit of a peculiar secretion in layers within the cells and tubes.

Previously to the elongation of the plumule, its point has acquired the rudimentary state of a leaf: this latter continues to develope as the plumule elongates, until, when the first

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