164 PHYLUM I. MYXOPHYCEAE 
217. In this Phylum the dominant idea is the simple 
nucleus, typically not limited by a nuclear membrane, 
asexual reproduction, and blue-green color. 
There are two classes: 
I. Nucleus not definitely outlined, no nuclear membrane; no 
plastids. Class 1. ARCHIPLASTIDEAE. 
II. Nucleus definitely outlined, with a nuclear membrane; 
plastids present. Class 2. HoLOPLASTIDEAE. 
Ciass 1. ARCHIPLASTIDEAE (CYANOPHYCEAE) 
Tue BituE GREENS 
218. In these plants (numbering about 2000 species) 
there is no limiting membrane around the primitive 
nucleus, and yet there is a simple karyokinetic process 
in cell division. In the absence of plastids the coloring 
matter is diffused throughout the cell. 
ORDER COCCOGONALES. UnIcELLULAR BLUE GREENS 
219. Here the plants are strictly unicellular, although 
they may be aggregated into colonies in which the cells 
are included in a gelatinous matrix due to the softening 
of their walls. 
220. These are the lowest and simplest of plants; they 
Q live as single cells in the water, or they may 
be aggregated into slimy films on sticks 
and stones. The principal family is Chro- 
ococcaceae, represented by minute species 
Fre. 60.— Of Chroococcus, Gloeocapsa, Aphanocapsa, 
Me cis mopedias Mferismopedia and other genera. Each cell 
> eer ne Pu divides into two, and these soon divide 
again, and so on. In Merismopedia the successive 
divisions are in two planes, resulting in quadrate 
colonies of regularly arranged cells. 
wnt 
