THALLOPHYTES 
mass, a characteristic bluish green color, quite distinct from the yellow- 
green color of the green algae. 1 
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. 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. 
8 Cloeothece 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. 
