254 GENERAL MORPHOLOGY OF PLANTS ' 



cells. They occur in fresh, brackish, or salt water, and on damp 

 rocks, soil, etc. A number of species have a preference for foul 

 water or waters which contain organic matter. Some of these on 

 decaying produce very foul odors, and sometimes occur in reser- 

 voirs for public water supply. Here they may become a great 

 nuisance and a menace to health. They can be destroyed by 

 adding small quantities of copper sulphate to the water in the 

 reservoirs without injury to the water for drinking purposes.* 

 Some of the blue-green algae are remarkable for growing in warm, 

 or hot, water, at a temperature which would prevent the growth 

 of other forms of plant life except certain bacteria. In the hot 

 water flowing from the geysers at Yellowstone Park some of these 

 algae live in water at a temperature of 

 58-68 C., or scantily at 75-77 C. 

 The blue-green algae multiply by division 

 of the cells and by breaking up of the 

 colonies or threads. In the filamentous 

 forms this division takes place much as 

 in spirogyra, by simple splitting or fission 

 of the cells. For this reason they are 

 sometimes called fission algae. See also 

 Giceocapsa. Bacteria, Chapter XXVII. Other char- 



acters are brought out in a study of the examples. 



388. Giceocapsa. This is a one-celled alga which forms thin 

 bluish-green patches on the ground or on rocks, logs, etc. Each 

 cell is roundish, and is surrounded by a thick capsule of a gelati- 

 nous nature which is stratified in distinct concentric layers. The 

 cells look as if they were enclosed in gelatinous capsules, hence 

 the name Giceocapsa. In multiplication the cells divide into two 

 daughter cells and these again divide in like manner. The divi- 

 sions take place in different directions, each cell having a distinct 

 stratified gelatinous envelope, and several of these enclosed for a 

 time in the envelope of the parent cell, which becomes larger with 

 the increase in the number of the cells. 



* See Bull. No. 64 Bureau of Plant Industry, U. S. Dept. Agr., 1904, and 

 Bull. No. 76, 1905. 



