CHAPTER XIII 

 THE GREEN ALGJE (CHLOROPHYCEJE) AND OTHER ALGJE 



173. General considerations. The green algae are found in 

 almost all inland -waters, floating freely upon the surface, ly- 

 ing in heavy mats near or below the surface, forming masses 

 upon the bottom, and often attached to various solid sub- 

 stances in the water. A few are marine in habit. They are 

 widely and abundantly distributed and may be found by any 

 observing student. Not infrequently they are spoken of as 

 " pond scums," " water mosses," and " seaweeds." 



Usually it is easy to distinguish green algae from most 

 other algae by the fact that in members of this group the 

 chlorophyll is not obscured by any other coloring matter. 

 Various shades of green are presented in different plants, and 

 indeed in the same kinds of plants at different growth periods, 

 but the color is not readily confused with that of the other 

 groups. 



174. Pleurococcus : structure and habitat. This green alga 

 grows in great abundance upon the partially shaded portions 

 of trees, fences, rocks, and old buildings, and when moist it 

 presents the appearance of a coating of green paint. Some- 

 times it is called " green slime." It adheres so closely to the 

 object upon which it grows that few people recognize it as a 

 plant. It is one of the most widely distributed of all plants. 



When examined under suitable magnification, it is seen that 

 the green slime is composed of thousands of single-celled 

 plants, each so small that as a separated individual it is not 

 visible to the ordinary observer (Fig. 155). A careful meas- 

 urement of a number of plants showed their average diameter 

 to be about ^Vo ^ an mcn (-014 mm.). In other words, if 

 a row of these plants side by side should be arranged across 



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