22 BOTANICAL GAZETTE [JANUARY 



roots." However, in describing the arctic vegetation (44, pp. n, 

 715), he follows the suggestion of KIHLMAN, a conclusion to which 

 he had come independently. GANONG (16) also accepts KIHLMAN'S 

 explanation for the xerophilous nature of the raised-bog flora of 

 New Brunswick. 



In the study of the structural adaptations of these plants and the 

 causes of their occurrence in bog areas, several questions arise. Are 

 these two factors, cold substratum and acidity, efficient causes of 

 xerophily ? Do they act, in the case of the bogs of this region, with 

 sufficient strength to cause xerophilous modifications in the plants 

 there found, or to permit the growth of only such forms as are xero- 

 philous ? 



The last question may be answered from field observations. 

 They indicate that most low-ground plants grow quite as well on the 

 bog substratum as on the ordinary swamp soils, and that the swamp 

 species of this vicinity may all be found at one place or another grow- 

 ing on bog soils. It would seem that here the bog substratum is no 

 more efficient as a selective agent than are the swamp soils. 



The only cases which have come under my observation in south- 

 ern Michigan which will throw light upon the question of the effect- 

 tiveness of the temperatures and acidity in the production of xero- 

 philous adaptations is in the case of Picea Mariana 1 and Pinus 

 Strobus. These two plants both show reduced size of stem and 

 leaf, in the Oxford bog, when compared with plants growing on the 

 margin. But to what extent this may be due to sterility of the 

 bog substratum rather than to temperature and acidity is indeter- 

 minable at this time. 



EXPERIMENTS. 



To answer the question of the efficiency of a cold substratum 

 and soil acidity to produce xerophily, experiments have been in 

 progress for approximately two years. The difficulties in the way 

 of experimentation along these lines are numerous. The means for 

 controlling soil temperatures in bodies of soil sufficiently large for 

 experimentation with the larger bog plants are practically beyond 

 the possibility of a university laboratory. When it is further realized 



7 The so-called P. brevifolia Pk. This form is certainly no more deserving of a 

 distinctive name than is the bog form of the white pine. 



