442 BOTANICAL SURVEY OF DISMAL SWAMP REGION. 



water. But as that is one of the most effective agents in the develop- 

 ment of adaptations against excessive transpiration in salt-marsh 

 plants, the xerophytie quality is naturally much less marked in the veg- 

 etation of fresh-water marshes. 



In the Fresh- Water Marsh formation it is principally the reed-like 

 monocotyledons which exhibit, adaptations that can be regarded as 

 protective against excessive transpiration and too intense light. The 

 position of the exposed leaf surface is chiefly concerned. The leaves 

 are often isolateral; they are usually orthotropic (vertical) or nearly 

 so; the margins are sometimes involute (Cladium, Kynchospora, 

 and numerous other sedges and many of the grasses), or the leaf is 

 even terete (species of Juncus); and in several cases, e. g., Iris, 

 Acorus, Xyris, Typha, the leaves are equitant, with edges opposed 

 to the greatest number of incident rays. The cuticle is often consid- 

 erably thickened. Hairy or waxy coverings, on the other hand, are 

 either wanting or so little developed as to he of slight protective 

 value. Neither the possession of leathery leaves with shining upper 

 surface nor of water-storage tissue (succulency) are characteristic of 

 this formation. 



The remainder of the Fresh-Water Marsh vegetation exhibits lit- 

 tle or no xerophytie structure. It is, indeed, for the most part 

 markedly hygrophile. The tall, reed-like plants afford the smaller 

 forms considerable shelter from son and wind, so that the majority of 

 them require no other protection against excessive transpiration. A 

 result of that exposure to the direct mechanical action of the wind to 

 which the vegetation of the larger marshes, unsheltered by tall woody 

 plants, is subjected is the development of much strengthening tissue 

 (stereome), noticeable especially in the stems and leaves of many of 

 the sedges, grasses, and rushes. 



The marsh vegetation is established upon a watery, incoherent soil 

 which would afford but a precarious footing to the plants were not 

 most of them especially fitted to hold themselves in place by their 

 strong, creeping, in many cases branching, rootstocks. This is con- 

 spicuous, as in the salt marsh formation, in the case of tall, heavy 

 plants like Typha latifolia, Eriatithussaccharoides, Scirpus cyperinus, 

 S. lacustris, Cladium effusuiu, etc. The richness of the substratum 

 in organic matter permits a dense, luxuriant plant covering, and thus 

 the danger to the individual plant of being uprooted is reduced to a 

 minimum. Some of the lower growing plants, being less liable to this 

 danger, have thick, comparatively short rootstocks, which are better 

 adapted to the storage of reserve food than to soil binding. Such are 

 Acorus calamus, Peltandra virginica, Pontederia cordata, Iris caro- 

 liniatia. Cicuta tnacalafa has a cluster of fleshy, dahlia-like roots. 



Water contains of course a smaller percentage of free oxygen 

 than docs the atmosphere. Consequently a soil rich in water is rela- 

 tively poor in free oxygen, and all the more so if the soil is acid. 



