426 BOTANICAL GAZETTE [DECEMBER 
2. Acidity—Much stress has been laid by various authors, 
following SCHIMPER (44, pp. 6, 18, 124), upon the acidity of the bog 
water as a factor in the bog habitat. In order to get a quantita- 
tive statement of the acidity for the bogs of this vicinity, a num- 
ber of 50°° samples have been titrated with an 1/100 solution of 
potassium hydrate Phenolphthalein was used as an indicator. The 
results show an acidity varying from .ooo1s5 to .00258 normal acid.* 
The lowest values are found in the areas occupied by bog sedges 
and by swamp plants, and they are practically the same. The areas 
occupied by cassandra and sphagnum have a somewhat greater 
acidity. The highest percentages are found beneath the tamaracks. 
The explanation of these variations in acidity is suggested by the 
tests, made from time to time, of the water in my experimental 
cultures. I found that the acidity of the water increased slowly in 
the undrained peat substratum cultures (see experiments). The 
increase was small in the case of the warm cultures, but quite notable 
in the case of the cold undrained substratum. On exposure to air 
in the water cultures, and in bottles, the acidity very slowly decreased, 
the decrease being greatest in the case of the water which was kept 
warm. This is probably due to increased oxidation. These relative 
amounts of acid, it will be seen, may be correlated with the tempera- 
tures in the several plant societies of the bog, the lowest temperatures 
corresponding to the highest percentages of acid. This suggests 
the probability that the acidity of the bog substratum increases 
farther north, 
On allowing open dishes of bog water to stand for some time, 
I found that the evaporation was not sufficient to raise the acidity of 
the water, oxidation apparently being more rapid than concentration 
of the solution. 
There is no apparent relation between color and acidity, although 
the lightest colored solutions usually show but slight acidity. This 
seems to indicate that only a part of the color is produced by free 
humus acids, the remainder by humates of the alkalies. 
solution: 
4 Following are the determinations expressed in fractions of a normal acid ‘ 
0o1lg, 
First Sister Lake: sedge zone, .00066, .ccog4; cassandra zone, .0015?, 
tamarack area, .00165, .00179, .00227, .00258; willow-sedge area, 00089, 0007? 
Chelsea; ditches, .00086, .ooors, .00043, .ooo19, and .00029. 
Delhi: tamarack area, .00146, cassandra zone, .oo117. 
Oxford: cassandra zone, .0009 4. 
