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. 



CLASS 1. ARCHIPLASTIDEAE (CYANOPHYCEAE) 

 THE BLUE 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 



* ^ ve as sni sl e ce ^ s i* 1 ^ ne wa ter, or they may 

 be aggregated into slimy films on sticks 



and stones. The principal family is Chro- 

 ococcaceae, represented by minute species 

 FIG. 60. of Chroococcus, Gloeocapsa, Aphanocapsa, 

 Chro^o^curSi Merismopcdia and other genera. Each cell 

 Gloeocapsa. 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. 



