444 BOTANICAL SURVEY OF DISMAL SWAMP REGION. 



divide the formation, and to follow this with a classification of the 

 ecological forms. These, like the systematic forms (as to genera and 

 families), arc, without exception, such as are widely distributed over 

 the face of the globe. 



COMPOSITION AND PHYSIOGNOMY. 



The greater part of the aquatic vegetation occupies bayous, ponds, 

 and ditches, where the current is very feeble or none is perceptible. 

 PhUoiria canadensis was the only truly aquatic embryophyte which 

 was observed to grow in the channel of the larger streams. 



Myriophyllum heterophylhnu and Castalia adorata are two of the 

 most abundant and characteristic water plants of the region, and are 

 often associated, especially in the numerous shallow pools which occur 

 in the open marsh land that borders the Dismal Swamp on the north. 

 The water lily is especially common, covering the surface of ponds 

 With its shining leaves and handsome white flowers. Both species 

 have strong rhizomes that creep in the mini at the bottom. Rut, while 

 the stout brittle stems of the Myriophyllum, often over 1 meter ^40 

 inches) long, rise above the surface of the water, Castalia usually 

 sends up its petioles and pedicels only so far that the fully developed 

 leaves and flowers float upon the surface. In Myriophyllum hefero- 

 phyllum the upper part of the stem, often to a length of '2 decimeters 

 (over (i inches), is emersed and bears simple, entire, or merely serrate 

 leaves, which are sharply differentiated from the finely divided sub- 

 mersed ones. Both Castalia and Myriophyllum prefer water that is 

 exposed, at least for some hours of the day, to direct sunlight. 



Nymphaea advena, which is sometimes terrestrial and then enters 

 the Heed Marsh formation, is often aquatic, with the habit of Castalia. 

 The handsome yellow lotus (Xelumbo Jaffa) was observed only near 

 Edenton, X. C, where it covered densely a shallow bayou opening 

 into Albemarle Sound. The great orbicular, peltate leaves either 

 float upon the surface of the water or are lifted considerably above 

 it upon elongated petioles. The pale yellow flowers are likewise 

 lifted above the surface. (Trowing among the petioles and pedicels of 

 Nelumbo were great quantities of free-swimming Spirodela polyrhiza, 

 which in other quiet waters of the region sometimes grows in nearly 

 pure association, spreading a sheet of green over the surface. 



Almost as important as Castalia ami Myriophyllum are species of 

 Utricularia, notably IT. purpurea and U. infiata, which are also plants 

 that grow best where their floating or emersed portion is exposed to 

 the sun's rays. U. purpurea is most abundant in ditches in the open 

 part of the Dismal Swamp, where it associates with Castalia odorata 

 or, in the recesses of the morass, with Sphagnum cuspidatum phtmo- 

 sum forma serrafa, and S. kearneyi. It often grows in such great quan- 

 tity as to obstruct navigation in the smaller canals by pole, paddle, or 

 wheel. The masses of steins and leaves, with innumerable swim blad- 



