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 reproduction 
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. Chlorophyll green plants with cellulose walls. 
Class 5. ConJUGATAR. 
II. Mostly yellowish-brown plants, with silicified walls. 
Cuiass 6, BACILLARIOIDEAE. 
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