. Introduction à la botanique systématique et structurel, et la physiologie végétale. La botanique. 62 LE DÉVELOPPEMENT GÉNÉRAL DES PLANTES, l'admirable mémoires de Nageli et de Braun sur l'une plantes unicellulaires, et les œuvres d'Ealfs, Kutzing, Thwaites, &c. sur le Desmidiacete Diatomacese, et illustrent une grande variété de formes. Le plus simple des cas, c'est que de 101. Les végétaux d'une seule cellule globulaires ; c'est, d'une cellule qui se développe de façon égale dans toutes les directions, et conserve donc la forme d'origine. Le microscopique plante connue comme donnant naissance au phénomène oired snow fournit une bonne illustration o

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. Introduction to structural and systematic botany, and vegetable physiology. Botany. 62 THE GENERAL DEVELOPMENT OF PLANTS, The admirable memoirs of Nageli and of Braun upon One-celled Plants, and the works of Ealfs, Kutzing, Thwaites, &c. upon the Desmidiacete and Diatomacese, illustrate a great variety of forms. The simplest possible case is that of 101. Plants of a Single Globular Cell; that is, of a cell which grows equally in every direction, and therefore retains the original form. The microscopic plant known as giving rise to the phenomenon oired snow furnishes a good illustration of the kind (Fig. 79, 80) : and so does a *° °' more common species, Protococcus cru- entus, which forms dull-crimson patches, resembling blood-stains, on the northern side of damp rocks or old walls. Each sphere is a single cell, which, quickly attaining its growth, produces (probably by division of the contents) a number of free cells in its interior. These escape by the decay of the walls of the mother-cell, grow speedily into similar cells or plants themselves, giving rise to another generation, and perish in their turn. Fig. 81 represents another and similar one-celled plant; and Fig. 82 and 83 show its mode of propagation, namely, by division of the whole living contents into two portions, and these again into two, these four globular masses soon acquiring a wall of cellulose, and becoming so many distinct cells or jjlants; — the whole process admirably illustrating a com- mon mode of cell-multiplication (30). Indeed, another microscopic plant of the kind, very common in shallow pools at the beginning of spring, was taken as the readiest example of this multiplication of cells (Fig. 18-22). This propagation causes the destruction of the mother-plant in each generation, all its living contents being em- ployed in the formation of the progeny, and its effete wall obliter- ated by softening or decay, and by tlje enlargement of the contained cells. Thus the simplest vegeta

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