THALLOPHYTES 



mass, a characteristic bluish green color, quite distinct from the yellow- 

 green color of the green algae.' 



The Cyanophyceae are found everywhere in fresh and salt water ; 

 and also on damp soil, rocks, bark, etc. A conspicuous free-floating 

 form gives the characteristic hue to the Red Sea, a fact which indicates 

 that "blue-green " algae may be red. They occur also in the water of 

 hot springs, thriving in a temperature that most other plants could 

 not endure. The sinter deposits which give character and attraction to 

 the craters of the hot springs and geysers of the Yellowstone National 

 Park, for example, are associated in some way with the presence of 

 Cyanophyceae. Many of the group are also endophytic in habit; that 

 is, they live within cavities of other plants, as in Anthoceros, Azolla, 

 roots of cycads, etc.; and still others 

 enter into the structure of those com- 

 posite organisms known as lichens. 



A general conception of the group 

 may be obtained by examining a few 

 common forms. 



Gloeocapsa.^ — The adult individual 

 is a single spherical cell (fig. 4), and 

 therefore the body is as simple as it can 

 be, if cells are to be regarded as the units 

 of the gross structure of plants. This 

 single cell consists of a protoplast invested 



Fig. 4. — Gloeothecc: a single 

 plant in the center, showing the pro- 

 toplast surrounded by the swollen 

 wall and a layer of mucilage; the 



by a wall, and among Cyanophyceae in other figures show various stages 

 general the protoplast has no such obvious °f cell-multiplication the cells 



° ' , being embedded in the gelatmous 



organization as among the true algae, matrix produced by their walls. 

 In general it may be differentiated into 



two regions: a peripheral zone, colored throughout by the green and 

 blue pigments; and a central region (central body), containing no 

 pigment, and now concluded to be a nucleus. In both regions small 

 granules appear. This differentiation of a pigment region from the 

 rest of the protoplast is not apparent among all the blue-green algae, 

 for in some (as Gloeocapsa) the pigments seem to be diffused through- 

 out the protoplast, but in others (as OscUlatoria, fig. 6) it is quite 



' The precise nature and relations of the pigment or pigments of this group are un- 

 certain. It is possible that there is a single pigment which splits into blue and green 



constituents. ■ . ,■ a ■ ■ 



2 Gloeothece is a fornj closely related to Gloeocapsa, from which it differs chiefly m its 



somewhat elongated cells. 



