314 GEORGE B. RIGG 



phytes seems to be explained .... by their ability to 

 adjust themselves to changed conditions without undergoing 

 a corresponding change in structure .... The .... 

 (xerophytic features found in some amphibious plants) were 

 developed when these species were growing in zerophytic 

 situations." 



h. They may be relicts from a former more general distribu- 

 tion of boreal plants under different climatic conditions than 

 we now have. This opinion has been expressed by Dr. H. C. 

 Cowles in his lectures. This view is also taken by Nichols 

 (35, pp. 215-216). Compare also Transeau (55, pp. 409-420). 



c. They may have been rendered xerophytic by bog condi- 

 tions. This view has been endorsed by Whitford (63, pp. 314- 

 315). Nichols (35, p. 212) says " . . . . soil conditions 

 satisfactorily account for the phenomonen of bog xerophytism 

 . . . ." Nilsson (without citation, possibly 35) is quoted 

 by Burns (1, p. 122) as attributing differences in structure be- 

 tween swamp and bog plants to a difference in the food supply. 

 It has been shown by Transeau (57, p. 867) that bog conditions 

 do to a certain extent induce xerophytism. It has also been 

 observed by the writer that Ledum and Kalmia grow much more 

 vigorously and show less of xerophytic appearance of their 

 leaves when growing outside of bogs than when growing in them. 



All of these theories must be considered in attempting to 

 account for the xerophily of the plants of sphagnum bogs. So 

 far as glaciated regions are concerned (a) seems to have much 

 weight, but when we remember that sphagnum bogs are not 

 confined to glaciated regions it is evident that careful considera- 

 tion must be given to (b) . The facts mentioned in (c) must also 

 be considered. 



HOW ARE PLANTS OTHER THAN BOG XEROPHYTES INHIBITED 



FROM SPHAGNUM BOGS? 



To the mind of the writer this question has much more inter- 

 est than the question just discussed. The following suggestions 

 -lave been made in regard to it. 



