I 



A SUMMARY OF BOG THEORIES 315 



a. "Physiological dryness/' because of abundant soluble salts 

 and humous acids. This is suggested by Schimper (52, pp. 4, 8, 

 and 658). It is approved by Dachnowski (18, p. 148). The 

 term "physiological dryness" is too indefinite to express any 

 exact factor. In so far as it might mean any chemical effect 

 of the acids or salts it is discussed in (6) and (c). In so far as 

 it might mean high osmotic pressm-e of the surrounding medium, 

 it is discussed in (e). 



b. Humous acids. This has received some support from Schnn- 

 per (52, p. 8) and from Warming (60). The writer knows of no 

 experimental evidence tending to estabUsh this as a factor. It 

 must be considered in the hght of the statement by Schreiner 

 (49, p. 579) that "humic acid" has absolutely no existence and 

 that the substance so called is a mixture of widely differing 

 compounds and in the light of the suggestion by Wieler (64) 

 that "humic acids" in soils are inorganic acids resulting, for 

 example, from the decomposition of salts. Skene (46) finds 

 that the sphagnums thrive best in acid solutions, since mineral 

 solutions, although generally physiologically harmless, may be 

 ecologically harmful. 



c. Soluble salts {e.g., Humus salts). This is also suggested 

 by Schimper (p. 658). So far as the writer has found this is a 

 mere suggestion, made without the evidence of any experimental 

 data. According to Schreiner (49, p. 579) the term "humates" 

 would also lose its meaning. 



d. Acidity as such (H ions). Negative experimental results 

 on this have been obtained by Livingston (33, p. 355) and a nega- 

 tive view of it has also been taken by Dachnowski (15, p. 132 

 and 16, p. 404). 



e. High osmotic pressure of the water in the substratum. 

 Whitford (63, p. 314) suggested that this might be a factor. 

 Negative results on this have been obtained by Livingston (32, 

 p. 385), and Rigg, Trumbull, and Lincoln (44), Transeau (58, 

 p. 37) and Dachnowski (15, p. 132 and 19, p. 505 and 510) 

 have also rejected this as being a factor of any considerable 

 importance. Dachnowski (16, p. 390) states: "During the 

 changes which the accumulated plant material undergoes in 



