THALLOPIIYTES 



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

 green coior of the green algae. 1 



The Cyanophyceae are found everywhere in fresh and salt water ; 

 and also on dam]) 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. 2 — 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 

 by a wall, and among Cyanophyceae in 

 general the protoplast has no such obvious 

 organization as among the true algae. 

 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 Oscillatoria, fig. 6) it is quite 



1 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. 



2 Gloeothece is a form closely related to Gloeocapsa, from which it differs chiefly in its 

 somewhat elongated cells. 



Fig. 4. — Gloeothece: a single 

 plant in the center, showing the pro- 

 toplast surrounded by the swollen 

 wall and a layer of mucilage; the 

 other figures show various stages 

 of cell-multiplication, the cells 

 being embedded in the gelatinous 

 matrix produced by their walls. 



