440 BOTANICAL SURVEY OF DISMAL SWAMP REGION 



Among other species that commonly occur in the low marshes are — 



Hydrocotyle umbellata. Ptilimnium capillaceum. 



Hydrocotyle ranunculoides. Limodorum tuberosum. 



Rhexia mariana. Gratiola tphaero oa v p a, 



Rhexia virginica. Gratiola virginica. 



Ludwigia linearis. Tlysanthes attenuata. 



Ludwigia alternifolia. Uysanthes gratioloides, 



Triadenum virginicum. Gerardia purpurea. 



Two white-flowered violets {Viola jirimulaefolia, V. lanceolata) are 

 likewise characteristic. Most of these plants begin to flower ahoul 

 midsummer, the violets being the principal vernal-flowering species. 

 Along the Dismal Swamp Canal, in moist, sandy, more or less inco- 

 herent soil, which has been heaped up in the process of excavation, 

 this formation is characteristically represented by — 



Carex verrucosa. Rynchospora axillaris. 



Juncus canadensis. Saururus cernutts. 



Juncus acuminatus debtlis. Panieum scabriusculum. 



Juncus repens. Jussiaea decurrens, 



Gypcrus erythrorhizos. Ludwigia alternifolia. 



Rynchospora glomerafa. Gratiola sphaerocarpa. 



A rank growth of Cyperus erythrorhizos 6 decimeters (2 feet) or 

 more high is shown in figure 84. Funaria hygromririca is an abun- 

 dant moss in the made ground along the canals in early May, but 

 entirely disappears before midsummer. Ferns, notably Osmunda 

 regalis and IVoodwurdia areolata, colonize the canal banks from the 

 neighboring swampy forest. 



On the margin of Lake Druinmoml, in the heart of the Dismal Swamp, there is 

 a small area of perhaps a hectare (2i acres) which is bare when the water level is 

 low. Here occurs an association in which tall plants of the Reed Marsh formation, 

 Scirpus cyperiitus criophorum and Erianthus saccharoides, mingle with Low 

 Marsh forms. In almost pure white sand at the very edge of the lake Juncus 

 repens is abundant, forming a short soft turf. Nearer the bordering woods the 

 soil is a wet muck, composed almost entirely of organic matter, and is somewhat 

 densely covered with a variety of species. Panieum yibbum, Panicularia pallida, 

 and Homaloeenchrus oryzoides are conspicuous and ecologically very similar 

 grasses. In midsummer the showy flowers, pale pink to deep rose color, of Rhexia 

 virginica and R, mariana, are the principal color element. Other species, notably 

 Junci. Hydrocotyle umbellata, Apios apios (tuberosa), and Decodon rerticillafus 

 help to complete the assemblage. 



ADAPTATIONS TO ENVIRONMENT IN THE FRESH-WATER MARSH — LIFE 



FORMS. 



The vegetation of the treeless marshes is exposed 1o certain condi- 

 tions which, in the palustrine forest, can greatly affect only the large 

 woody plants and the epiphytes. These are — 



1. The direct heat and light of the sun, as opposed to diffused light 

 and radiated heat. 



L\ The unbroken mechanical and physiological action of air currents. 



