424 BOTANICAL GAZETTE [DECEMBER 



and percolation are at a minimum. It is well known that when salt 

 solutions are passed through soil, much of the salt is retained by 

 absorption. The relative amount is greatly increased in the case 

 of humous bodies. BLANCK (4) has further found that the diffusion 

 of water in humus soils is decreased by the presence of acid humus 

 compounds, and that this may be corrected by the addition of a 

 neutralizing agent, such as lime. All analyses of peat show how little 

 of this mineral matter has been derived from the adjacent soils. It 

 is only in the case of samples taken from the bottom or edge of a bog 

 that the mineral salts cannot be accounted for by the amount derived 

 from the decay of the plant material, and that obtained from the 

 atmosphere. 



6. Water-capacity. The high water-capacity of peat has already 

 been noted. In relation to plant growth, it is detrimental in that it 

 prevents proper aeration of the substratum (39, p. 346). So far as 

 the diffusion of gases is concerned, such substrata are less favorable 

 than a free water surface. King (29, p. 161), in speaking of sand 

 and clay soils whose water-capacity is only 17.5 to 32.2 per cent, 

 by weight, says that 30 to 40 per cent, of their saturation amounts 

 must drain away before the soil can contain air enough to maintain 

 the respiration of roots and germinating seeds. As compared with 

 a free water surface, saturated humus cannot admit oxygen as freely, 

 owing to the large part of the surface actually occupied by the humus 

 (29, p. 239). In a chemical way it is still more effective, as will be 

 noted later. 



7. Osmotic pressure. The osmotic pressure of bog waters has 

 been found to be about the same as that of ordinary lakes and rivers. 3 

 They are approximately 'equivalent to a o.i to 0.5 per cent, normal 

 Knop's solution. They indicate quite certainly that bog plants do 

 not ow r e their distribution and their peculiar structures to a high 

 osmotic pressure of the bog water. 



3 Four samples of bog water from this vicinity were tested by Dr. B. E. LIVING- 

 STON, of the University of Chicago, and found to have the following pressures in milli 

 meters of mercury at 25 C.: 



First Sister Lake, Sample A . 50.0742 



First Sister Lake, Sample B 40.0593 



We?t Lake, Sample A 100.1484 



West Lake, Sample B 150.2226 



Lake Michigan water 100.1484 



See 33, 



