WATER REQUIREMENT AND ADAPTATION IN EQUISETUM 3 



determining factor in the bog habitat is the ratio of the possible 

 rate of water absorption to the rate of transpiration, and that 

 the toxicity of the bog habitat has a primary role in bringing 

 about bog conditions." From his study of cultures of isolated 

 bog bacteria he concludes that bacterial toxins are the leading 

 factor to be considered in the physiological aridity of bogs. 



Rigg, (1913: 310) from his investigation of the effect of bog 

 waters on the root -hairs of Tradescantia, suggests that "the 

 toxins act through their stunting effect on root-hairs." In 

 other words, plants which grow in bogs can have only a low 

 absorptive power. 



The conclusion of these writers is that the xerophily of bog 

 plants is due to the toxic effect of the habitat. 



{2) Xerophytic nature due to persistence of stable structures 



Clements (1905: 126) holds the view that many of the so- 

 called swamp xerophytes are not xerophytes at all, but are 

 plants which have developed their xerophytic features while 

 growing on dry land. They have subsequently been able to 

 adjust themselves to present conditions without undergoing a 

 corresponding change in structure. His view is based upon the 

 presence of hydrophytic structures in the plants and the 

 association of the plants with typical hydrophytes. 



(3) Winter xerophily among plants 



Gates (1914: 445) has made a very thorough study of the 

 nature of the evergreen heaths growing in bogs, principally 

 Chamcedaphne, and concludes that "in view of the fact that 

 exposure to the very extreme summer conditions in 1911 and 

 1912 did not affect the vitality of the evergreen ericads, that 

 neither did the average winter of 1910-1911, with its scanty 

 snow covering during the coldest weather, while the extreme 

 winter of 1911-1912 killed the parts of the evergreen ericads 

 which projected above the snow; and in view of the fact that the 

 evergreen habit is hereditary, that the position of the leaves in 

 winter is different from that in summer, and that the trans- 



