40 



COMPENDIUM OF GENERAL BOTANY. 



A frequently discussed example (discovered and studied by 

 PKINGSHEIM) is the growth in length of the alga Oedogonium. 

 Here we are not concerned simply with a localized surface growth 



23 4 



FIG. 19. Division of a desmid-cell (diagramatic). 



of a cylindrical membranous zone ; the complication therein lies in 

 the fact that the inner layer of the zone is undergoing active growth 

 while the outer layer of the same zone becomes torn (Fig. 20). 



First the cellulose-ring is formed, projecting inward (w). The 

 smaller Fig. 20, B, represents the time-period at which the circular 

 tearing of the outer membrane has taken place 

 (w'\ and the elongation of the cell takes place 

 at the expense of the cellulose-ring. After 

 elongation is completed a new septum forms. 

 Repetition of this process gives rise to the 

 " caps " represented in the larger figure (five 

 caps at c in Fig. A), and a corresponding 

 number of sheaths, which are directed upward, 

 are formed by the projecting edges of the 

 repeatedly ruptured cell- wall. These sheaths 

 are just separated from each other, and each 

 one lies in the vicinity of a transverse septum. 

 Besides the instances already mentioned 

 there are a series of growth phenomena 

 belonging to this category, as is evident from 

 the consideration of those spongy and stellate 

 tissues in leaves and water- 

 plants. Primarily all cells 

 are in close contact. Three 

 cells may enclose an inter- 

 cellular space (i, Fig 21), 

 which space is the result of 

 peculiar localized surf ace - 

 growth of the cell-membranes. 1 



"We have been obliged to mention some very important cell- 



FIG. 20. (After Sachs.) 



FIG. 21. 



1 Compare ZIMMERMANN'S Beitrage zur Morphologic uud Physiologic dcr 

 Pflanzenzelle, Heft 3, 1893. 



