120 



INTEODtrCTION TO CRYPTOGAMIC BOTANY, 



Ralfs.* All agree in their increase by the partition of the 

 mother ceU, accompanied by the growth of two new half cells 

 (Fig. 30, a. b.). In many cases, the division goes no further, but 

 each half, with its new lobe grows into a perfect whole, and 



Fig. 30. 



a. Micrasterias denticulata, Br6b. 



h. Scenedesmus quadrioaudatus, Turp., after Mr. Ralfs, both shewing 

 the origin of the new half cells. 



c. Threads of Nostoc verrucosum, after Thuret. 

 All more or less magnified. 



Fig. 31. 



Pe7iium Jenneri, 

 Ealfs, -ndth its spore 

 magnified. From 

 Mr. Ealfs. 



Fig. 32. 



Closlerium aculum, 

 Br6b., free and in 

 conjugation, magni- 

 fied. From Mr. 

 Ealfs. 



Fig. 33. 



a. Eiiastrum ele- 

 gans, Kiitz. 



b. Spore of the 

 same, magnified. 

 From Mr. Ealfs. 



* Ealfs' British Desmidiacese, 8vo. 1848. 



