504 BOTANICAL GAZETTE [December 



The evaporation in a bog forest averages 8.1 cc. daily and shows 

 a close correspondence to the record obtained by others for a beech- 



■ 



maple forest. 4 In a bog meadow the rate (10. 9 cc. daily) is less 

 than that for the open campus of the State University (15.8 cc. 

 daily). As far as local atmospheric conditions are concerned, the 

 rate of evaporation is not a sufficient cause to determine succession 

 of vegetation, nor are the differences in the rates efficient limiting 



factors. 



The role of substratum temperature is obviously not the most 

 direct factor in southern localities contributing to the causal rela- 

 tion between water requirements of bog plants and available supply. 

 Neither has the coefficient of the differences between soil and air 

 temperatures a greater value in the selection of plants for bog areas, 

 or in their root functions. 



The concentration of mineral salts in bog water from various 

 plant associations ranges between 40 and 160 parts per million; 

 the acidity of the solutions varies from less than 0.00075 to 0.004 

 normal acid, when titrated with NaOH. There seem to be no free 

 "humus" acids. The acid reaction noted can be attributed to 

 adsorption phenomena, 5 especially to the selective absorbent power 

 of the cell colloids of disintegrating plant tissue which retain, as 

 Baumann and Gully 6 have shown, chiefly the basic ions of dissolved 

 salts. The osmotic pressure of the solutions in the various associa- 

 tions is very nearly alike in the several plant zones and about the 

 same as that of lake and river water. The differences cannot be 

 associated with factors limiting the distributional relationships 

 and the activity of plants in bogs. 



Variations in the position of the water table do not influence 

 the character of the vegetation, nor do they offer an explanation of 

 the xerophytic structure of the plants, for the peat mat upon which 

 the more typical bog xerophytes and heath associations succeed 

 one another is more often a floating mat and moves with any change 



*Transeau, E. N., The relation of plant societies to evaporation. Bot. Gaz. 

 45:217-231. 1908. 



Fuller, G. S., Evaporation and plant succession. Box. Gaz. 52 : 193-208. 191 1. 



• • 



s Cameron, F. K., The soil solution. 1911. p. 55. 



6 Baumann, A., und Gully, E., Uber die freien Humussauren des Hochmoores. 

 Mitt. K. Bayr. Moorkulturanst. 1010. pp. 31-56. 



