ALGAE — MEIER < 419 



foul conditions. The " salty sea odor " so much loved is largely 

 due to stranded seaweed or marine algae. 



The best way to eliminate odors and tastes produced by algae in 

 lakes, ponds, reservoirs, and other standing bodies of water, is to 

 control the growth of the water plants, in the place concerned. 

 Numerous methods have been devised to accomplish this, some of 

 which are: Keduction of the available food supply, or by so modi- 

 fying the chemical composition of the water that it will not support 

 large growths of algae; poisoning the organisms by the addition 

 of chemicals to the water; and control of the physical factors that 

 affect the growths. The use of copper sulphate as an algicide has 

 become standard practice. Ordinary commercial crystals of blue 

 vitriol are placed in a coarse bag or gunny sack. The container is 

 attached to a rope and drawn zigzag back and forth across the water 

 at the stern of a rowboat. Organisms differ considerably in their 

 susceptibility to copper sulphate. Some of the blue-green algae 

 are destroyed by the application of only 1 part of copper sulphate 

 in 10,000,000 parts of water. 



The rice fields of southern Spain and Samarkand with their irri- 

 gation ditches contain numerous algae characteristic of tropical and 

 subtropical flora found in sluggishly flowing water or in hard, 

 strongly mineralized waters of pools and bogs (pi. 1, fig. 1). These 

 algae demonstrate their ability to withstand great differences in 

 temperature changes during the day. The daily temperatures vary 

 in June and July from 68° to 99° F.; in August and the early part 

 of September from 61° to 84° F. The increase and decrease of algal 

 forms are proportional to the periodicity of the irrigation. 



In a large body of fresh water, as was found to be true in the 

 central African lakes, a single sample of the algal flora obtained in 

 a stated locality cannot be regarded as representative of that of the 

 entire lake. Collections of algae made within a few days of each 

 other from different parts of Tanganyika differ radically even in 

 their dominant type of flora. It seems probable that in large lakes 

 the different species of algae occur in large shoals of more or less 

 limited extent. 



Algae are common in torrential brooks and rivers (pi. 2, fig. 2). 

 The river may possess its own typical algal flora, or algae may 

 be carried into it from springs, pools or ponds, lakes, canals, or 

 tributaries. The factors governing the algal production in a river 

 are the rate of flow, the detritus content, the quantity of water, 

 the chemical constituents, and the temperature. Except in certain 

 very large rivers, the swifter the current, the less the algae. 

 As a river flows through various lakes the algae of the river are 

 modified by the lake through which it passes, just as the algae 



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