VEGETATION OF THE HIGH DUNES. 379 



etc., mingle with or take the place of the pine. At Cape Henry occur 

 thickets of laurel oak (Qaercus laurifolia), mostly .'5 to 3^ meters (10 

 to 12 feet) high. 



The ground being shaded and protected from the wind by the trees, 

 a small amount of humus collects on the surface of the inner dunes, 

 giving the soil a gray color (hence "gray dunes," one of the terms by 

 which they are known in Europe).' Here, among the pines, the live 

 oak (Quercus virginiana) attains ils best development on the Vir- 

 ginia coast, although in this region it, is never of arboreous size and 

 shape. Quercus virginiana assumes on the wooded dunes a compact, 

 rounded, symmetrical form, with nearly horizontal branches, very 

 different from its aspect among the open dunes. The largest speci- 

 men seen was about 8 meters (25 feet) high, about 8 meters in great- 

 est spread of branches, and the diameter of the largest stem 3 deci- 

 meters (1 foot) above the ground was nearly (J decimeters. The live 

 oak grows scatteringly among the pines, not forming thickets. In 

 the dull, dark color of its foliage it resembles Myrica carolinensis. 



On the summit and outer slope of the fixed dunes Ammophila are- 

 naria is still abundant, sometimes carpeting the ground to the exclu- 

 sion of other herbaceous vegetation ; but apparently flowers are rarely 

 if ever produced in this situation. Doubtless it was this grass which 

 contributed most to the original fixing of these dunes and their prep- 

 aration for other vegetation; and one might fancy that the plant is 

 reluctant to yield its sway to less hardy species. Panicwii amarum 

 minus and Cyperus grayi are common on the fixed dunes. With the 

 latter C. cylindricus, of similar habit, frequently occurs. But the 

 most characteristic herb of these dunes is Galium hispidulum, which 

 has slender yellow root stocks branching and creeping through the 

 sand in every direction at a depth of usually 2 to 4 centimeters (1 or 



2 inches), while sending up at frequent intervals clusters of leafy and 

 flowering stems, commonly only 8 or 10 centimeters (3 or 4 inches) 

 high. 



Quite different is the type of vegetation normally occupying only 

 the inner slope of the forested dunes, but occasionally extending over 

 the crest and down the outer slope. Here prevails a dense 1ow t under- 

 growth of chiefly woody species, some of which do not venture farther 

 into the strand formal ion. In a typical place Sassafras sassafras and 

 Xanthoxylum clava-her cutis, the latter attaining here a height of onlj T 



3 to decimeters (1 to 2 feet), were particularly abundant. Smilax 

 bona-noXy S. glauca, Vitis aestivalis, Tecoma radicans, and Partheno- 

 cissus quinquefolia formed dense tangles among the low shrubs. At 

 other points Ilexopaca, Rubus cuneifolius, Aralia spinosa, Call icarpa 

 arnericana, and even Acer rubrum and Nyssa sylvatica, enter into 

 this association. 



1 Warming, Okologisohe Pftanzengeographie, p. 24-3. 



