CHAPTER IX 



PHYLUM III. ZYGOPHYCEAE 



THE CONJUGATE ALGAE 



249. These plants are typically unbranched, unat- 

 tached filaments, which easily fragment into short 

 segments, or single cells. They are green, with chloro- 

 phyll, but in many cases this is obscured by the presence 

 of a yellow-brown pigment in the cells. They propagate 

 by the fission and ultimate separation of cells (hormo- 

 gones) or by the formation of spores, but are wholly 

 destitute of zoospores. They generate by the union of 

 the protoplasm of pairs of ordinary cells (isogametes). 



250. The dominant idea in this phylum is the physio- 

 logical sluggishness of the cells, resulting in the feeble 

 attachment of the cells to one another and the easy and 

 usually early fragmentation of the filament, the absence 

 of zoospores, and the reduction of the sexual roi)roduction 

 to the sluggish union of the scarcely modified proto- 

 plasms of two vegetative cells. This is a phylum on the 

 down-grade, and all of its members show more or less 

 structural degeneration. 



There are two classes: 



I. Chloroi)hyll p;rceii phiiits with cellulose walls. 



Class 5. CONJUGATAE. 



II. Mostly yellowish-brown plants, with silicificd walls. 



Class G. Bacillarioideak. 

 12 177 



