77 



Contents of both conjugating cells uniting in one of the original 



cells. ZYGNEMACE.E. 



Contents of the conjugating cells uniting in an intermediate cell. 



MESOCARPE.E. 



171. Of various forms, hut mostly with a central contraction forming 

 symmetrical halves. Cell contents bright green. Wholly destroyed 

 by a strong heat or by strong mineral acids. DESMIDIACE.E. 



Cell contents yellowish or orange. Cytioderm or cell skeleton con- 

 sisting mainly of silica, so that the form and the beautiful char- 

 acteristic markings remain after the decay of the cell contents, 

 or their destruction by fire or acids, but completely dissolved by 

 caustic alkalies. Cell contents turned green by death or by acids, 

 but not changed by alkalies. DIATOMACEJB. 



Rabenhorst's classification of the Diatomaceae, Diatomophyceae, or 

 Bacillarise is given in 174. 



172. Microscopic, one-celled plants of a bright-green color, but occa- 

 sionally red or orange. Cells often associated in clusters so as 

 to appear like a single body. Cells or cell clusters frequently 

 contained in mucus. Mostly growing in fresh water or on wet 

 substances. 173 



Cells of a dull green, blue-green, or brown color, single or associated 

 in threads or variously-shaped clusters. Some species have an 

 unpleasant odor. Gyanophycece or Phycochromophycece. 



Truly branching. SIROSIPHONIACE^:. 



Not branching, or only apparently branching ; but sometimes spread- 

 ing from a common sheath. 



One-celled plants. Cells single, or many associated in clusters, and 

 contained in a common covering, surrounded by mucous matter. 



CHROOCOCCACE.S. 

 Many-celled plants. Cells divided in only one direction. 



Vegetation limited at the ends of the threads. Threads jointed, 

 slender at the upper extremity, often drawn out to a long thread- 

 like point; provided at base with a persistent vegetative cell. 



RlVULARIAC&S. 



Vegetation not limited at the ends. 



