﻿Nichols: The vegetation of Connecticut 211 



acteristic of xerophytes ; while analogous xerophytic modifications 

 may frequently be observed in the leaves of bog-grown individuals 

 of such a species as Alnus rugosa, which occurs in both types of 

 swamps. The xerophytic peculiarities of the leaves of bog ever- 

 greens, e. g., the Cassandra, however, need not necessarily be 

 attributed to the nature of the habitat, but may rather, to a certain 

 extent at any rate, be associated with protection frorn excessive 

 transpiration during the winter.* 



Many theories have been advanced with a view to explaining 

 the condition of physiological xerophytism prevalent in bogs. It 

 has been variously ascribed to the acidity of the soil, to the low 

 temperature of the soil, to the insufficient aeration of the soil, and 

 to the accumulation in the soil of root excretions or various toxic 

 substances.f Doubtless there are still other factors whose efifect 

 may be equally potent. For example, in view of the low diffusion 

 properties of humus soils, which to a great extent would exclude 

 salts derived from the subjacent mineral soil, together with the 

 only partial decomposition of vegetable remains in bogs, it is 

 conceivable that an actual scarcity in the bog substratum of the 

 requisite mineral elements in form suitable for absorption and 

 assimilation by most plants may be a factor of some significance. 

 Indirectly, the topographic relations of bogs are considered im- 

 portant. Bogs usually develop in undrained or poorly drained 

 depressions, and almost invariably in connection with a water 

 body of considerable depth. In Salisbury, Norfolk, Kent, Litch- 

 field, and elsewhere there are bog-bordered lakes, but in many 

 cases, the depressions occupied by bogs, although quite deep, are* 

 only a few acres in extent. In two small bogs at Southington, for 

 example, the writer was unable to touch bottom with a twenty-five 

 foot peat sampler. One of these bogs is shown in FiG. 15. That the 

 lack of drainage in such basins would tend to promote soil acidity, 

 poor aeration, and the accumulation of deleterious substances 

 seems obvious, while their depth would favor low soil temperatures. 

 Regarding the relative importance of these different factors, how- 



* See Gates. F. C. Winter as a factor in the xerophily of certain evergreen 



