BLUE-GREEN SEAWEEDS 
HE minute alge, which form patches of purple color on 
rocks, slimy layers or spots on wharves, bluish-green slime 
on mud, emerald-green films on decaying alge, blue-green 
slime on brackish ditches, and so on, are various species of the 
subelass Cyanophycez. The prevailing color of these plants is 
blue-green, but some are purple, brown, or pink. Some of them 
are gelatinous in texture and shapeless, others have more definite 
forms ; but all are too small to classify without the aid of a power- 
ful glass, and are not of special interest except to the botanist. 
GENERA Oscillaria and Spirulina 
The genus Oseillaria is so named from an oscillating move- 
ment which these filamentous plants show when viewed under 
the microscope. They are very delicate blue-green threads occur- 
ring singly, or in loose or felt-like floating masses, or like slime 
or scum, on mud or woodwork. In Spirulina the filaments are 
spirally twisted like a corkscrew and also have a vibrating move- 
ment. Spirulina is often found growing with Oscillaria, and 
forms purple patches on wharves. 
Genus Calothria 
( Beautiful hair") 
Filaments one tenth of an inch long, terminating in transparent 
hair-like points, occasionally branching. The plant grows in fine 
tufts or like a fringe on alge or in patches on rocks. Sometimes 
it forms a spongy layer, again a velvety stratum. The color 
varies in different species; it may be bright green, brownish- 
4 49 
