11. BOG XEROPHYTES AND ACID SOILS. 



The true nature of bog and swamp plants that possess apparent 

 xerophytic structures has been a subject of discussion since Volkens 

 and Zingeler first observed the protected stomata of many hydrophytic 

 species of Carex. The concept of bog xerophytes was definitized by 

 Warming (1895) and by Schimper (1898), the latter regarding them 

 as outstanding examples of physiological drought. This interpreta- 

 tion was first questioned by Clements (1905, 1907), who showed that 

 the transpiration and growth of certain so-called bog xerophytes were 

 those of hydrophytes. Since this time a number of studies have 

 dealt with this problem (Yapp, 1909; Sampson and Allen, 1909; 

 Gates, 1914; Folsom, 1918; Dosdall, 1919; Bergman, 1920; Clements 

 and Goldsmith, 1921), with the result that the number of supposed 

 bog xerophytes has steadily decreased. In the series of investiga- 

 tions under way it is hoped to make a comparative study of the water- 

 relations of the majority of bog and swamp plants that have been 

 regarded as xerophytes, and consequently to ascertain the real 

 significance of their xeromorphic characters. 



THE NATURE OF BOG XEROPHYTES. 



Earlier views. — The first observations on the discrepancy between 

 structure and habitat were made by Volkens (1884 : 23; cf. Zingeler, 

 1873 : 127). It was found that certain species of Carex, e. g., C. 

 glauca, gracilis, limosa, maxima, panicea, and paniculata, possessed 

 stomata with papilliform projections that extended from the accessory 

 cells over the openings, forming a chamber protected from dry air. 

 Volkens stated that from all the analogies this adaptation must serve 

 as a device against excessive transpiration, and yet it was charac- 

 teristic of species without exception that thrive only in wet soil. 

 Moreover, this protective device was found to be absent in the 

 species of dry soil. He sought to explain why sedges growing in wet 

 soil should reduce water-loss by covering the stomata by the fact 

 that the ground-water sank in midsummer, thus causing a certain 

 amount of drought in the upper layers. 



Warming (1888 : 125) showed that several swamp species of Carex 

 exhibited the same structure of the leaf as that found in pronounced 

 heath-plants, such as Carex nardina and Elyna hellardi. As a conse- 

 quence of the lack of harmony with the habitat, he was inclined to 

 regard the structure of the leaves as the common heritage of the 

 group MonostachycB, which was independent of the habitat. 



From a study of the stomata of certain grasses and sedges Schwen- 

 dener (1889 : 76) concluded that the structural characters which are 



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