CRYPTOGAMS 



171 



New filaments arise from short portions (Jiormogonid) with rounded 

 ends (Fig. 283, li), when these portions have been set free from the old 

 filaments. 



283. Oscillatoria: a, i^art of a filament showing hormogonia {h, h) ; c, 

 filaments, less magnified. 



413. The Blue-green Algae comprise a large number of species, 

 many of which differ considerably in general habit from the forms 

 just described. 



GREEN ALGJE 



414. The Green Algse (so called from tlieir pure 

 chlorophyll green color) are mainly small aqnatic plants, 

 and chiefly inhabit fresh waters ; though some of them 

 are sub-aerial. The smallest members are distinguishable 

 only with the microscope ; the largest form growths 

 several inches in diameter. ^ The exceedingly numerous 

 species vary widely in structure and mode of life. The 

 few here described will give some idea of the chief types. 

 It should be understood at the outset that only the most 

 important facts of life history are given ; and that in 

 many of the forms modes of reproduction, not here de- 

 scribed^ exist. 



415. Pleurococcus. — Almost all surfaces that are occa- 

 sionally wet and are not too much exposed to heat and 

 drying — as shaded sides of tree trunks, rough posts, and 

 rocks — after a time become 

 green by the growth of mi- 

 nute unicellular plants of vari- 

 ous kinds. They thrive and 

 multiply in i-ain and dew, and 

 resist ordinary drying. One 

 of the commonest of these unicellular forms is Pleuro- 

 coccus (Fig. 284). The plant is simply a microscopic 



28i. Pleurococcus. 



For example, the familiar Sea Lettuce of the seashore. 



