86 PROCEEDINGS OF THE ACADEMY OF [Marcll,. 



rock, at least of the valley in which the pond lies, is limestone, and 

 the glacial drift contains abundant fragments of calcareous rocks; 

 the pond is fed by springs arising through limestone, so that its 

 water is subalkaline, and similar reactions are shown by the waters 

 at various places in the swamps along the stream draining the pond. 

 Marked differences in flora, in so far as its members, are sensitive 

 to soil reaction, would be expected to appear on comparing these 

 two regions. 



Ericaceae (used in the broad sense) are actually far more abundant 

 in the Dover region, forming dense thickets; and two of them, 

 Kalmia latifolia and Vaccinium corymhosum, become small trees. 

 Clethra almfolia, Euhotrys racemosa, and Gaultheria procu7nbens may 

 be noted as species which grow here btit appear to be absent at 

 Green Pond. Noteworthy members of families other than Ericaeae 

 present in some abundance are: Sniilax rotundifolia, Habenaria 

 psycodes, Coptis trifolia, Spiraea tomentosa, and Ilidoides mucronata; 

 all these are absent or rare at Green Pond. To those who are sus- 

 ceptible to Rhus poisoning, the Dover swamps will be found far 

 more pleasant than the Green Pond ones, for in the former R. vernix 

 and R. toxicodendron are very rare. 



While the water of the Green Pond swamps is more or less alka- 

 line in reaction, soils of definite and even high acidity are also pres- 

 ent there, in the form of hummocks and mounds of decaying vege- 

 table matter mingled with sphagnum and other mosses. On as- 

 cending these the reaction becomes less alkaline, passes through 

 neutrality, and often reaches mediacid character at the top. The 

 Ericaceae growing in this swamp are exclusively limited to such 

 mounds. The species noted comprise: Azalea nudiflora (rare); 

 A. viscosa; Kalmia angustifolia; Xolisma ligusirina; Gaylussacia 

 haccata (rare) ; Vaccinium corymhosum; and Vaccinium macrocarpon. 

 The soils of these were found to range from mediacid to subacid, 

 their roots apparently not extending into material so moistened by 

 the swamp water as to have less acidity than this. Notable plants 

 of other families showing the same relations are : Cypripedium acaule, 

 Coptis trifolia, Menyanthes trifoliata, and Linnaea borealis var. 

 americana. 



On the other hand there are here a number of plants which grow 

 entirely or chiefly in soils bathed by the alkaline water, and ranging 

 from neutral to subalkaline in reaction. Such are Cypripedium hir- 

 sutuni (reginae), C. candidum, Betula pumila, Caltha palustris, Par- 



