220 PLANT PHYSIOLOGY 



It is greatly to be regretted that those organisms which 

 apparently transgress the general laws expressing the rela- 

 tions of active protoplasm to heat have been so little 

 studied by physiologists. The vegetation of geysers and 

 hot-springs, and of the very cold waters from glaciers and 

 persistent snow-deposits, has been studied too exclusively by 

 systematists. The temperatures of the waters are known 

 only in a general way, the temperature of the water actu- 

 ally bathing the organisms and the exact condition of the 

 organisms have not been accurately determined.! Each 

 actively fermenting manure-heap, each mass of organic 

 matter so rapidly decomposing that high temperatures 

 develop in it (e.g. where hay "heats" in cock or mow), is 

 the seat of bacteria, the optimum temperatures of which are 

 above the maxima for most forms. The difficulty of suc- 

 cessfully imitating the natural conditions hampers experi- 

 mental study of these organisms. 



Continental bodies of land are subject to considerably 

 wider extremes of temperature than prevail in oceanic 

 islands and in certain limited and peculiarly situated areas 

 near the coast. These show limited ranges of temperature, 

 but it is possible to cultivate there plants which naturally 

 occur much farther north or south. This is partly the rea- 

 son why semi-tropical and decidedly northern plants can be 

 successfully cultivated in the region about the Bay of San 



* See Pfeffer's Pflanzenphysiologie, Bd. II., p. 87, 1901. 



f Davis, B. M. Vegetation of the hot-springs of the Yellowstone Park. 

 Science. VI., 1897. Tilden, J. E. Observations on some West American 

 thermal algre. Bot. Gaz., vol. 25. 1898. 



