LIKE FORMS OF THE HYGROPHILE FOREST. 429 



the shade of the Mack Gum forest, nor are they common where 



Arundinaria is most abundant. 1 



In the swampy woods that border streams a few kilometers west of 

 the main body of the Groat Dismal Swamp a number of species enter 

 into the Black Gum forest association that, were not observed farther 

 east. The tree growth remains the same; but, among shrubs, the 

 fringe tree {Chionanthu* virginica), cornel {Cornus candid Issima), 

 elder (Sambucus canadensis), and Viburnum dodatum are common. 

 Lilium superlmvi on hummocks and old stumps grows to a height of 

 nearly 2 meters (0 feet), bess frequent is Habenaria cristata with 

 small (lowers of a brilliant orange color. 



Along brooks, especially when flowing through cleared land, occur 

 small specimens of a number of trees that arc comparatively rare or 

 altogether wanting in the large wooded swamps. Noteworthy are the 

 button wood {Platmms occidenkdis), black cherry (Prunus scrotum), 

 and Catalpa bignonioides, associated with small examples of-cypress 

 (Taxodium), red maple {Acer rubrurn), and other species common in 

 the palustrine forest. 



ADAPTATIONS TO ENVIRONMENT IN THE HYGROPHILE FOREST -LIFE 



KOIiMS. 



An analysis of the physical environment that prevails in this type 

 of forest leads to the segregation of certain factors which are known 

 to be of primary importance in their influence upon plant life: 



1 . High temperatures during at least six months of the year, a com- 

 paratively mild winter, and, consequently, a long growing season. 



2. Strong light, during a great part of the growing season, the annual 

 percentage and number of hours of sunshine being relatively high. 



3. Abundant atmospheric humidity and a heavy rainfall, fairly 

 equably distributed throughout the year. 



4. Absence of exposure, for the most part, to strong winds. 



5. Soil very wet, usually saturated, often covered with 3 decimeters 

 (1 foot) or more of standing water; cold; poor in oxygen; more or 

 less acid; exceedingly rich in partially decomposed organic matter. 



To the soil conditions all t he vegetation, save the epiphytic and para- 



' Lesquereux, in a paper entitled ' ■ Torf bildung im grossen Dismal Swamp," pub- 

 lished in Zeitschr. der deutschen geolog. Gesellsch., vol. 4, pp. 695 to 01)7 (1852), 

 ascribes a much greater importance to Sphagnum in the Dismal Swamp than it 

 really possesses. He writes of the vegetation as " consisting, as in Switzerland 

 chiefly of Sphagnum, of which, besides European species, there occur several 

 which are peculiar to this continent." This author is surely in error when he 

 interprets the swamp. with its central lake, as an example of "that lacustrine 

 peat formation which occurs in the great bogs of Scandinavia and Denmark. 

 There he states, "whenever the covering which overlies the underground lake 

 becomes too heavy it sinks easily and gradually, first in the middle and then 

 toward the periphery." W e have no evidence that Lake Drummond was produced 

 in any such way. 



