322 GEORGE B. RIGG 



h. By changing the permeability of the protoplasts. This 

 has been suggested by Dachnowski (19, pp. 513, 514, and 21, 

 p. 62) and is in accord with the current conception of the way 

 in which toxins act on plants. 



Although much of the literature cited in this paper deals also 

 with the physiographic history of bogs, no attempt has been 

 made to review the literature of that phase of the subject. The 

 writer has chosen to confine his attention in this paper to an 

 effort to systematize the matter relating to the xerophily of the 

 plants characteristic of the particular physiographic phase for 

 which he has suggested a definition at the beginning of this 

 paper and to the large inhibition of mesophytes from this phase. 



The literature listed at the end of this paper includes only 

 the papers to which citations have been made. While care 

 has been taken as to the accuracy of the citations and no effort 

 has been spared to make them complete, it is scarcely to be hoped 

 that the list is free from errors or omissions. 



The writer acknowledges with pleasure his indebtedness to 

 Prof. H. C. Cowles for several conferences on bog problems, 

 and to Prof. William Crocker for suggestions in regard to the 

 literature on toxicity. 



LITERATURE CITED 



(1) Burns, G. P. A botanical survey of the Huron river valley. VIII. Edaph- 



ic conditions in peat bogs of southern Michigan. Bot. Gaz. 52 : 105- 

 125. 1911. 



(2) Bauman, a. and Gully, E. tJber die freien Humus Sauren des Hoch- 



moors. Mitt. K. Bayr. Moorkulturanst. 4: 31-56. 1910. 



(3) Backman, F. F. The plasmatic membrane and its organization. New 



Phyt. 11 : 180-195. 1912. 



(4) BoERGESEN, F. Nogle Eric. Haars. Udvikl. in Bot. Tidsskr. 17: 307-314. 



1890. 



(5) BoTTOMLEY, W. B. The significance of certain food substances for plant 



growth. Ann. Bot. 28: 531-540. 1914. 



(6) Breifeld, a. Der Anatomische Bau der Bliitter der Rhododendroideae 



in Beziehung zu ihrer systematischen Gruppierung und ihrer geo- 

 graphischen Verbreitung. Leipsig, W. Englemann. 1888. Engler 

 Jahrb. 9: 319. 



(7) Clements, F. E. Plant Physiology and Ecology. New York. 1907. 



(8) CoviLLE, F. V. The agricultural utilization of acid lands by means of 



acid-tolerant crops. Bull. 6 I". S. Dept. Agr. 1913. 



