16 



ELEMENTARY STUDIES IN BOTANY 



the development of increasingly complex bodies, is for the 

 cells to become unlike. This tendency to become different 



FIG. 8. Cladophora: 

 a branching fila- 

 ment, each of whose 

 cells contains several 

 nuclei ; in two of 

 the cells swimming 

 spores have devel- 

 oped, and from one 

 of the cells some of 

 the spores have es- 

 caped, showing the 

 pair of cilia. 



FIG. 9. Laminar ia : a 

 common kelp, show- 

 ing a complex body 

 differentiated into 

 holdfast, stalk, and 

 blade (leaf-like por- 

 tion). 



is called differentiation. For example, in the filamentous 

 body of Ulothrix (Fig. 7, A) the lowest cell differs from all 



FIG. 10. Macrocystis: a kelp with very 

 long and rope-like stem bearing nu- 

 merous blades. After BENNETT and 

 MURRAY. 



