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 w/ioo solution of 

 potassium hydrate Phenolphthalein was used as an indicator. The 

 results show an acidity varying from .00015 to .00258 normal acid. 4 

 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. 



4 Following are the determinations expressed in fractions of a normal acid solution : 

 First Sister Lake: sedge zone, .00066, .00094; cassandra zone, .00152, .00119; 

 tamarack area, .00165, .00179, .00227, -00258; willow-sedge area, .00089, .00072. 

 Chelsea: ditches, .00086, .00015, .00043, -00019, and .00029. 

 Delhi: tamarack area, .00146, cassandra zone, .00117. 

 Oxford: cassandra zone, .00094. 



