320 GEORGE B. RIGG 



He does not suggest this with I'eference to bogs but the idea 

 seemed to the writer to be worth consideration in that connec- 

 tion. Rigg, Trumbull, and Lincoln (44) found no evidence for 

 considering this a factor since the surface tension of all bog waters 

 tested was much greater than the value (0.68 of that of distilled 

 water) which Czapek determined to be the surface tension of 

 plant protoplasts. 



q. Toxic substances in the substratum. This was suggested 

 by Livmgston (32, p. 385; 33, pp. 354-355) and experimental 

 evidence to support it has been furnished by Dachnowski (15, 

 p. 141; 16, p. 403; 17, p. 339; 20, p. 318) and by the writer (41, 

 p. 318). Transeau (58, p. 38) finds that " . . . . local 

 (Michigan) bog water has no tendency toward the production 

 of xerophilous modifications." The large amount of varied 

 experimental evidence on this theoiy leads the writer to regard 

 toxicity of the water as a very large factor in the inhibition from 

 bogs of plants other than bog xerophytes. The writer has found 

 experimental evidence (43) tending to indicate that colloidal 

 matter in the water is a large factor in its toxicity. 



r. Bog plants are more plastic than other plants (Dachnowski 

 19, p. 513). 



s. Bog plants in contact with peat soil may cause the injurious 

 organic compounds to be precipitated in insoluble form w':^ile 

 other plants do not have this effect (Dachnowski 19, p. 514). 



WHAT^( ARE THE POSSIBLE SOURCES OF THE TOXIC SUBSTANCE 

 OR SUBSTANCES IN BOG WATER? 



a. Excretion products of subterranean portions of higher 

 plants. Dachnowski (15, p. 141 and 16, p. 403) has suggested 

 this. 



5. Products of the metabolism of bacteria, fungi and proto- 

 zoans. Dachnowski's (19, p. 513) work on bacteria in bogs 

 suggests this. 



c. The decay of sphagnum moss. The writer (41, p. 324) 

 has called attention to the fact that since the presence of sphag- 

 num moss and the lack of drainage are the two conditions neces- 



