HOW TO KNOW THE FRESH-WATER ALGAE 



aquatic plants, and others as well, may be allowed to age and to be- 

 come discolored in dishes of water in the laboratory. The endophytes 

 (and some epiphytes too) will then appear more clearly and can be 

 dissected away for study. 



In humid climates trunks of trees and surfaces of leaves may have 

 epiphytic or endophytic (semi-parasitic) algae such as Tientepohlia 



The habitats of freshwater algae are very diverse, some 

 living in hot springs where the water is nearly at boiling 

 temperature; others in snow banks in high mountains; 

 whereas one alga normally occurs on the back of the 

 snapping turtle. 



and Cephaleuios. Arisaema (Indian turnip) leaves invariably contain 

 the parasitic alga, Phylfasiphon, which causes yellow or red spots in 

 the host tissues. 



One interesting habitat is the back of snapping turtles where the 

 coarse, wiry filamentous alga, Basicladia is invariably found. Other 

 algae may be associated with Basicladia on the 'mossy' backs of 

 turtles, whereas alligators are sometimes veritable algal gardens and 

 offer a variety of interesting forms for the less timid collector. In the 

 rain-forests of the tropics, Central America, e. g., the three-toed sloth 

 harbors among its hair scales a minute red alga, Cyanoderma hiady- 

 podis, and a filamentous green alga, Trichophilus welcheii. 



In alpine and subalpine regions where there are banks of per- 

 manent snow, red streaks will be found at the margins of the snow 

 fields. The streaks are produced by the unicellular green alga, Chla- 

 mydomonas nivalis which contains a red pigment (haematochrome) 

 which is developed in the cells when they are exposed to intense 



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