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. Biancx (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 4o 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.* 
They are approximately equivalent to a 0.1 to 0.5 per cent. normal 
Knop’s solution. They indicate quite certainly that bog plants do 
not owe 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. Livinc- 
STON, of the University se ae and found to have the following pressures in milli- 
meters of mercury at 2 
First Sister ie pene A. 6  soores 
First Sister Lake, eer Be a a eee 
West Lake, — ple ee ne a ee a ee 
West race Sample B i ae a ee 6 
Lake Middgnwaier © (6) 6 °° ° 2 22 so0.24Be 
See 33. 
