CRY proa Aiis 



171 



New filameiits arise from short portions (Jwrmogoniu) witli rounded 

 ends (Fig". 2S:j, A), wlien tliese portions have been set free from the old 

 fihiineiits. 



28.'.>. Oscillat(,iria: <', part of a filament slio\\ing hunnogouia (ft, /t) ; c, 

 filaments, less magnified. 



413. The DUie-green Algu^ comprise a large number of species, 

 many of wliich differ considerably in general habit from the forms 

 just described. 



GREEN ALGiE 



414. The Greefi Algie (so called frofii their pure 

 chlorophyll greeti color) are mainly small aquatic plants, 

 and cliieHy inhahit fresh waters ; though some of them 

 are sub-aerial. The smallest members are distifiguishal)le 

 only with tlie microscope ; the largest form growths 

 several inches in diameter. ^ The exceedingly numerous 

 species vary widely in structure and mode of life. The 

 few here descriljcd will give sotne idea of the cliief types. 

 It should be uuderstood at the outset that onl}' the most 

 important facts of life history are given ; and that in 

 luany of the fortiis 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 truidvs. rough [losts, and 

 rocks — after a time become 

 green by the grcjwth of mi- 

 nute unicellular plants of vari- 

 ous kifids. They thrive and 

 multiply ill rain and dew, and 

 resist ordinary drying. One 

 of the commonest of these unicellular forms is Pleuro- 

 coccus (Fig- 284). Tlie plant is simply a microscopic 



St. Pleurococcus. 



1 For example, the familiar Sea Lettuce of the scashcire. 



