Rennert : The PiivLLonES of Oxvpoi.is filifokmis 407 



polls does not owe its peculiar structure to an adaptation to wet 

 and dry periods, but that it is a true swamp or bog xerophyte in 

 accordance with the generahzation of Schimper, who supposes that 

 the water of bogs and swamps contains such a large proportion of 

 humic acid as to render absorption difficult. Plants growing in 

 such places therefore have difficulty in securing a requisite supply, 

 as if growing under arid conditions. Not all plants are capable of 

 absorbing water from a mixture exhibiting a higher pressure than 

 that of the cell-sap of the absorbing organs. 



Dr. Shaw * has pointed out that the vegetation of a pond in 

 its final stage is always xerophytic and has drawn attention to the 

 fact that the continual deposit of organic material around the mar- 

 gin of a pond will produce a zone so much filled with humic acid 

 as to be entirely devoid of vegetation. Dr. Cowles f has upheld 

 this view of the xerophytic character of an undrained swamp and 

 has frequently noted the remarkable assemblage of xerophytic 

 adaptations such as leathery or hairy leaves and special structures 

 for water absorption exhibited by the flora of peat bogs. In con- 

 firmation of this standpoint Dr. Cowles has pointed out that if 

 plants growing in swamps of this type are xerophytic we ought 

 to find them thrving in dry regions. And this he reports to be 

 true ; Clcthra alnlfolla, Spli'aca touicntosa and Myrlca ccrlfera, gen- 

 erally conceded swamp plants, have been found thriving and in 

 all respects normal on dry hillsides.^ 



As Briquet has indicated, the most superficial examination of 

 the plant brings to light the unmistakably xerophytic character of 

 the reduced leaf-surface and the strong development of hypoderm. 

 On the other hand many of the characters which Briquet regards 

 as demonstrating the hydrophytic nature of the plant, seem when 

 viewed in the light of recent ecological work, to be adaptations 

 either for water storage or the prevention of transpiration. The 

 large thin-walled empty celled endoderm certainly exhibits capac- 

 ity for water storage. The thick cuticle and the waxy incrustation 

 of the epidermis, the accessory cells and the sunken position of 

 the stomata, and the presence of resin glands all point to the con- 



*Shaw, C. H. The Development of Vegetation in the Morainal Depressions of 

 the Vicinity of Wood's Hole. Bot. Gaz. 33 : 437. 1902. 

 f Cowles, H. C. Bot. Gaz. 27 : 293. 1899. 



