BLUE-GREEN SEAWEEDS 



minute algae, which form patches of purple color on 

 _L rocks, slimy layers or spots on wharves, bluish-green slime 

 on mud, emerald-green films on decaying algae, blue-green 

 slime on brackish ditches, and so on, are various species of the 

 subclass Cyanophycese. 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 Oscillaria 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 Calothrix 



C" 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 algae 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- 

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