434 HOTANICAL SURVEY OF DISMAL SWAMP REGION. 



surface of soil or water. An interesting peculiarity of the knees in this 

 region is that they appear as if still living long after the destruction 

 of the tree which produced them, another evidence of the preservative 

 effect of the swamp water. 



Arching of the larger roots which lie on or near the surface of the 

 soil is a peculiarity of both Taxodium and Nyssa biflora. (Pis. LXTX, 

 IjXXIII). Tn case of the former it is the initial step to knee forming, as 

 these projections seem always to form Ihe summits of root arches. 

 One cypress root, which was examined had 1 meter (nearly 4 feet) of 

 its length raised above the surface of the ground, to a maximum 

 height of 2« r ) centimeters (S inches). The arches are usually, however, 

 shorter and rather higher. In Xyssa biflora such a striking develop- 

 ment of arched roots as that figured by Shaler 1 was not observed. 

 In both species the roots above ground are more or less compressed 

 laterally. It is possible that the elevation of such arched portions of 

 the root above the surface of the substratum is, like the development 

 of pneumatophores, useful to the plant by aerating the underground 

 parts of the root system, but exact knowledge on this point is 

 wanting. 



Distension or tumidity of the basal part of the trunk, already men- 

 tioned, is a peculiarity common to most of the larger swamp trees, 

 although more conspicuous in Taxodium and the two species of 

 Nyssa {biflora and aquatica) than in other species. Shaler, who 

 discusses this question at some length in the paper just quoted, is 

 inclined to regard the swollen base as physiologically homologous 

 with the pneumatophores and arched roots, i. e.,as an aerating struc- 

 ture. It seems more likely, however, that the principal object is to 

 secure to the tree a firm foundation in the watery, often unstable soil. 

 The fact that most large forest trees, although growing in soils not 

 deficient in oxygen, are more or less enlarged at base, argues for the 

 explanation of this phenomenon on mechanical principles. 



"Juniper" (CJta maecyparis f-hyoi,<le,s), is, from an ecological point of 

 view, chiefly remarkable in that, while always a hygrophile species, 

 often growing in standing water, it exhibits none of the just described 

 structures for facilitating respiration in the subterranean parts. It 

 possesses neither knees nor projecting, arched roots, and the trunk 

 is either not swollen at base, or not as much so as in most ordinary 

 forest trees. 



OTHER ECOLOGICAL, CHARACTERS. 



The preponderance of woody over herbaceous vegetation, character- 

 istic of most parts of the Non-Hygrophile forest, is even more strongly 

 accentuated in the wooded swamps. In the most typical areas, e. g., 

 the Black Gum swamp near Lake Drummond, almost all the ombryo- 

 phytic plants have their steins more or less lignified. Even the ehar- 



Loc. cit., p. 324, tig. 83. 



