120 



INTRODUCTION TO CRYPTOGAMTC BOTANY. 



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

 mother cell, accomiDanied by the gro^vth of two new half cells 

 (Fig. 30, a. h.). 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, Brub. 



h. Scenedesmus quadricaudatus, Turp., after Mr. Ealfs, both shewiiit 

 the origin of the new half cells. 



c. Threads of Nostoc vernicosum, after Thuret. 

 All more or less magnified. 



Fig. 31. 



Penium Jenneri, 

 Ealfs, with its spore 



magnified. 

 Mr. Ralfs. 



From 



Fig. 32. 



Clostermm acutum, 

 Breb., free and in 

 conjugation, magni- 

 fied. From Mr. 

 Ealfs. 



Fig. 33. 



a. Euastrum eJe- 

 gans, Kiitz. 



b. Spore of the 

 same, magnified. 

 From Mr. Ealfs. 



* Ealfs' British Desmidiaceae, 8vo. 1848. 



