76 



CHLOROPHYCEAE 



balls that they float to the surface. Their characteristic shape is 

 brought about by a continual rolling motion over the soil surface 

 under the influence of wave action, and hence the "ball" forms are 

 found near the shore whilst the "thread" and "cushion" forms 



^^^iiwvw*,^^ 



Fig. 52. Cladophora. A, ball of Aegagropila holsatica cut through and the dirt 

 removed ( x |). B, same before cutting ( x |). C, C glomerata, commencement 

 of septum formation. D, C glomerata, second stage in septum formation. 

 E, C glomeratum, septum almost complete. F, diagram illustrating evection. 

 G, H, types of branching. I, C. glomerata, structure of wall at a septum. 

 J, Spongomorpha coalita with hook branches. K, C. callicoma, structure of chloro- 

 plast with nuclei and pyrenoids. L, Ae. Sauteri, zoospores in zoosporangium. 

 M, Ae. Sauteri, zoospores. (A, B, after Acton; C-K, after Fritsch; L, M, after 

 Nishimura and Kanno.) 



are to be found farther out in deeper water where there is less 

 motion. The harder the floor the more regular is the shape of the 

 balls, but even so the ball structure would also appear to be inherent 

 in the alga because "balls" have been kept in a laboratory for eight 

 years without losing their shape. The following types of branches 



