108 



of hackbeny, Ccltis occidentalis, probably forty or fifty years old. 

 Under it are shrubs of apple, Cormis Bailcyi, and Rosa sp. They 

 are overhung with vines of Pscdera quinqiicfolia, and in their shade 

 are plants of Polygonatitm coinmutatiun. Many other common sand 

 plants are associated with them. It is probable that all these species 

 were introduced by birds, since they all have fleshy fruits. Vitis vnil- 

 pina, Mcnisperuium canadcnsc, Fopulus dcltoidcs, and Acer Negiindo 

 were reported by Gleason (Hart and Gleason, igoy: i68) for sim- 

 ilar conditions in the Havana area. 



Although these three blowouts have no species in common, the 

 vegetation probably represents the first stages, chang'ed considerably 

 by proximity to civilization, of a definite series. This series, how- 

 ever, has always been curtailed by refilling the blowouts with sand, 

 since there is no association in the three areas mentioned which can 

 possibly be referred back to this origin. 



THE STKNOPHYLLUS ASSOCIATION 



It has already been mentioned that a thin layer of loamy soil is 

 formed on the surface of the sand in the bunch-grass association. 

 This layer is coherent and quite resistant to wind action. The depos- 

 its of a blowout may bury this soil layer to a considerable depth and 

 for an indefinite time, completely destroying the original vegetation. 

 At a suljsequent period another blowout may develop on these depos- 

 its and finally expose the old soil layer. When this is uncovered the 

 growth of the blowout in depth ceases. Its future growth, if any, 

 is lateral, leaving a flat bottom which is level or gently sloping. 

 Blowouts of this type are generally easily recognized by the bottom 

 being flat instead of the usual concave shape. As soon as the soil layer 

 is uncovered a new type of vegetation appears, characterized partic- 

 ularly by the small sedge Sfciiophyllus capiUaris, and constituting the 

 Stenophylhis association. 



This is well illustrated by several blowouts in the Hano\er and 

 Oquawka areas. One in the former (PI. XI, Fig. i) is of special 

 interest since it shows the old soil over the western half of the blow-- 

 out, while the other half is still pure sand, with the usual vegetation. 

 The western half is flat, but slopes up about one foot (3 dm.) in its 

 total width of 25 feet (8 m.), indicating the gently rolling nature 

 of the original surface. The soil layer is covered with one to two 

 inches (2-4 cm.) of fresh sand, blown in from an active blowout 

 toward the west. This portion of the blowout is occupied by numer- 

 ous small tufts of Sfoiopliylliis about an inch (2-4 cm.) wide, a 



