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Principles of general and comparative physiology : intended as an introduction to the study of human physiology : and as a guide to the philosophical pursuit of natural history / by William B. Carpenter, M.D.

  • Carpenter, William Benjamin, 1813-1885.
Date:
1841
Catalogue details

Licence: Public Domain Mark

Credit: Principles of general and comparative physiology : intended as an introduction to the study of human physiology : and as a guide to the philosophical pursuit of natural history / by William B. Carpenter, M.D. Source: Wellcome Collection.

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    in the centre of the nucleus, are the only permanent ones. § § 407-9, 429. 2. The simplest form of Reproduction,—that which exists in the lowest Cryprocami1a,—differs but little from the ordinary mode of multiplication by cells. The whole plant may consist of a reproductive cell, as is the case in the lowest Alge and Fungi; or special reproductive cells may be evolved from some particular portion of it. In either case, the granules contained in these cells develope themselves into new cells, which are capable of living by themselves: and from these, in a greater or less time (according to its degree of complexity) the new plant is evolved. Every new cell, as it is formed, constitutes a part of the permanent structure ; and this is composed, in the lower Cellular plants, of single rows of vesicles. In the higher forms of this division, however, the first nisus is towards the develop- ment of a foliaceous expansion, the whole of which remains as the permanent frond constituting the perfect plant. This is well seen in the Hepatice. 88 593-7. 3. In the highest Cryptogamia, such as the Ferns, the repro- ductive cells (or spores) form but a very small proportion of the whole structure. When these are liberated from it, the first nisus is the same as in the Hepatice ; a foliaceous expansion, con- sisting merely of cells developed from the germs contained in the reproductive cell, is first formed, and to this the name of primary frond has been given, The permanent structures, how- ever,—the stem bearing the rudiments of the true leaves, and the true roots,—originate only in the centre of this. The peripheral portion, which merely serves for the temporary support of the young plant, by absorbing water, carbonic acid, &c., from the air, then decays away. §§ 597, 615. 4. In the Puanerogamia, the germs of new cells, contained in the pollen-grains, are conveyed, by a peculiar means, into receptacles, the ovules, which do not exist in the Cryptogamia ; in these they are supplied with nutriment already prepared for organisation. Their first nesus of development is, however, the same as in Cellular Plants. The cells produced from the granular germs contained in the pollen-grain, compose a folia- ceous expansion (the single or double cotyledon), which has for its object, as in the Ferns, the temporary support of the young plant,—partly by the absorption of the albumen supplied to it in the ovule, and afterwards by performing the functions of leaves