428 BOTANICAL GAZETTE [DECEMBER 



(3). Furthermore, it has been shown that when soil rich in nitrogen 

 is saturated with water so as to exclude free oxygen, denitrification 

 takes place and nitrogen gas is set free (29, p. 115). 



The phosphoric acid content is comparable with that of the best 

 soils, and it is at least partially in a condition for plant use. 



The potassium content is very low. Analyses and the results 

 of agricultural experiments show that in order to produce crops this 

 substance must be added, and preferably in an alkaline form. Inquiry 

 among the owners of onion marshes in this vicinity confirms the need 

 for potassium in local bog soils. 



The amount of calcium present is reported as equal to that of 

 the best upland soils. But it is probable that as it exists under 

 natural conditions in bogs it is bound up largely in insoluble humates. 

 Under the influence of oxidizing processes it would become available 

 to the plants at the surface. 



When we consider the conditions under which the various plant 

 societies in our bogs exist and their competition with one another, 

 there can be little doubt but that the substratum varies in each case 

 as to its chemical composition. That the societies may be classified 

 on a physiographic basis is certain, but how to determine the chemical 

 factors accompanying each physiographic change is an unsolved 

 problem. The ordinary methods of analysis give us the minerals 

 present, but tell us little about their form and availability for plant 

 assimilation. The colorimetric methods for determining the quantity 

 of mineral salts present in bog water are mostly open to objection. 

 The ease with which the humous bodies of the bog water are decom- 

 posed render their quantitative estimation by present methods of 

 little value. Yet it seems probable that work upon the chemistry 

 of humus and humous compounds must result in data valuable alike 

 to the ecologist, the forester, and the agriculturist. 



C. BIOTIC FACTORS. The interrelations of the bog species will 

 be discussed in connection with their other ecological characters. 

 It will be sufficient to mention here that they are with a few excep- 

 tions light- demanding forms. Consequently, size and ability to 

 produce shade are the important factors in their competition with one 

 another. 



A second element enters into this problem of the struggle between 



