. Practical botany. Botany. THE GREEN ALG.^ (CHLOROPHYCE^) 205 of calcareous material, which, as the plant dies, falls to the bottom of the pond or stream. V]i<n-a grows in such luxuri- ance that its deposits eventually form deep layers of this cal- careous material, or marl as it is called. jMarl has been found of great value in the manufacture of cement, and not a few of the lakes in \\hich Chara grows are being dredged to secure the marl deposits for this important manufacture. 188. Algae and water supply. Many of our large cities have found it advisable to construct reservoirs for water
. Practical botany. Botany. THE GREEN ALG.^ (CHLOROPHYCE^) 205 of calcareous material, which, as the plant dies, falls to the bottom of the pond or stream. V]i<n-a grows in such luxuri- ance that its deposits eventually form deep layers of this cal- careous material, or marl as it is called. jMarl has been found of great value in the manufacture of cement, and not a few of the lakes in \\hich Chara grows are being dredged to secure the marl deposits for this important manufacture. 188. Algae and water supply. Many of our large cities have found it advisable to construct reservoirs for water. These are open pools, lakes, tanks, etc., and they are intended to hold water enough so that in times of scarcity there will be at hand a sufficient supply. Such reser- voirs have proved so admirable as growing places for algse that these plants have often become a nuisance. Their presence in water for domestic use is not at- tractive, and, besides, they may stop up the water pipes ; but far more serious than these objec- tions is the actual pollution of the water because of their pres- ence. When they die they be- come the food for decay-produc- ing organisms (Sect. 154), and often positively injurious sub- stances may thus be generated. It has been found that by tow- ing about in such reservoirs a quantity of copper sulphate, inclosed in coarse sacking, minute quantities of the salt be- come dissolved and the algse are thus killed. The solution is not strong enough to render the water unwholesome for Fig. 168. Desmids A,Micrasterias: B, B', Staurastmm (two views); C, Closterium. Aftei' West. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Bergen, Joseph Y. (Joseph Young), 1851-1917; Caldwell, Otis William, 1869- joint author. Boston, New York [etc. ] Ginn and company
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