62 THE GENERAL DEVELOPMENT OF PLANTS, 



The admirable memoirs of Nageli and of Braun upon One-celled 

 Plants, and the works of Ralfs, Kutzing, Thwaites, &c. upon the . 

 Desmidiacese and Diatomaceae, illusti-ate 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 thei'efoi'e retains the 

 original form. The microscopic plant 

 known as giving rise to the phenomenon 

 of red 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, resembUng 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 plants ; — the Avhole process admirably illustrating a com- 

 mon mode of cell-multiplication (3G). Indeed, another microscopic 

 plant of the kind, very conunon in shallow pools at the beginning of 

 spring, was taken as the readiest example of tliis 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 the enlargement of the contained 

 cells. Thus the simplest vegetation goes on, from generation to 

 generation. The softened remains of the older cells often accumu- 

 late and form a gelatinous sti'atum or nidus, in Avliich the succeeding 

 generations are developed, and from which they doubtless derive a 



FIG. 79. Several individuals of the Red-Snow Plant (Protococcus nivalis) magnified. 80. 

 An individual highly magnified, showing more distinctly the new cells or spores formed with- 

 in it. 



FIG. 81. An individual of Chroococcus rufescens, after Nigeli, much magnified. 82 A 

 more advanced individual, with the contents forming two new cells by division. 83. Another, 

 with the contents divided into four new cells. 



