SOME EXAMPLES OF ALGAE 



201 



pleasant way at times, when, after multiplying very rapidly during 



the hot summer, they die suddenly in the early fall and leave their 



remains in our water supply. Much 



of the unpleasant taste and odor of 



drinking water comes from this cause. 

 Some examples of algae. One of 



the simplest algae is Pleurococcus 



(pl6o-ro-kok'#s). This little plant 



consists of a single tiny cell, which 



by division may give rise to two or 



more cells which cling together in a 



mass. The green color on tree trunks, 



stone houses, etc., is often due to 



millions of these little plants. 



Spirogyra, a pond scum, is known 



to every boy or girl who has observed 



a small pond or sluggish stream. It 



grows as a slimy mass of green threads 



or filaments. Under the low power 



of the microscope, the body is seen to 

 be a filament made up of elongated 

 cylindrical cells, each of which con- 

 tains a spirally wound band of chlo- 

 rophyll. Spirogyra may reproduce 

 ..cytoplcxsm asexually by division of the cells. It 

 may also reproduce sexually. When 

 this happens, the cells of two adjoin- 

 ing filaments push out portions of their 

 cell walls which meet, forming a bridge. 

 The cell walls in the middle of the 

 bridge dissolve. The protoplasm of 

 the cells thus joined condenses into 

 two tiny spheres, and ultimately the 

 contents of one cell passes through 

 the connecting tube and mingles with 

 the cell of the neighboring filament. 

 This process by which two cells of 



eel \/afl 



.— nucleus 

 fC^if..chloropla5t 



a single cell 



a colony 

 of Wo 

 OeMs 



anot 

 a colony 

 of four 

 cells 



Pleurococcus. Explain how a colony 

 of Pleurococcus might come into ex- 

 istence. 



chlorophyll 

 loandL 



.nucleus 



..cell ^ccll 



. ..vacuole 



A single cell of Spirogyra. Is the cell 

 flat or round in cross section? 



