316 GEORGE B. RIGG 



the process of peat making there are alterations and reductions 

 leading to gaseous and colloidal products but little known." 

 The writer (43) has found that there is a considerable amount 

 of colloidal matter in filtered bog water. 



The thesis that in general, the relations between plants and 

 the soil are chiefly determined by the concentration of the soil 

 solution and the limits within which it may vary has been de- 

 fended by Gola (12) and (27). He contrasts the colloidal and 

 the crystalloidal characters of the soil. 



/. Low temperature of the substratum. This was suggested 

 by Kihlman (31) and has received support from Friih and Schroe- 

 ter (23), Transeau (57, p. 867 and 56, p. 358-360), and Cox 

 (11, p. 222), and is discussed by Burns (1, p. 110). It has been 

 rejected by Transeau (58, p. 364) as being inadequate to account 

 for conditions in the bogs of southern Michigan. Dachnowski 

 (18, pp. 138-139) does not beheve that the topographical dis- 

 tribution of plants in bogs can be accounted for on the basis 

 of low temperatures of the substratum. Transeau (58, p. 36) 

 has noted that low temperatures may retard chemical action, 

 diffusion .and osmosis and keep down bacterial action. The 

 evidence from Cox's work (10, pp. 45, 82, 119) is that low soil 

 temperature is an important factor. 



g. Low temperature of the air over the bog. The observa- 

 tions of Burns (1, pp. 108 and 110) and of Cox (10, pp. 46, 81) 

 indicate that this is a factor. 



h. Difference between air temperature and soil temperature. 

 Dachnowski (18, p. 139) decides that this is not a factor of suf- 

 ficient importance to enter into the problem. It was suggested 

 by Transeau (55, p. 419). Cox's dat^ (10, pp. 69, 78, 82) seem 

 to indicate that it is an important factor. 



i. High evaporating power of the atmosphere {e.g., drying 

 winds). This has been suggested by Kihlman (31) as acting 

 in connection with (/). Dachnowski's (18, pp. 143-144) ex- 

 perimental evidence is unfavorable to this view. Cox's data 

 (10, pp. 98-109) are also unfavorable to it. The situation of 

 many of the bogs in the Puget Sound region makes it evident 

 that this is probabty not an important factor in them. 



