168 



and numerous species of the bunch-grass may also spring up, 

 but a new group of species appears, and by their predominance 

 the aspect of the vegetation is entirely changed (PL XV.). 



Among the first to appear is Stenophyllus capillaris, which 

 grows in a carpet over the flat bottom of the blowout, but 

 never extends up the sloping sides. Its growth soon results in 

 the formation of a thin layer of black humus over the surface. 

 Associated with it usually are large clumps of Panicum iirg/i- 

 tum and Sorghastrum avenaceum. These grasses are typical 

 plants of damp blowouts and interdunal depressions, but re- 

 tain their place even when the blowout is subsequently cov- 

 ered by blow-sand. Andropogon furcatus, another grass com- 

 mon on the black-soil prairies, is frequent, and with these her- 

 baceous species are often associated a number of woody forms 

 not found at all in the bunch-grass prairie or in the black-jack 

 timber. These are Vitis vulpina, Menispermum canadense, Popu- 

 lusdeltoides (PI. IX.), and Acer Negundo (PI. XVII. ). AH of 

 these have effective methods of seed dispersal, and are probably 

 disseminated widely over the sand area, but are able to effect 

 ecesis only in these more favorable conditions. The two vines 

 scramble over the ground, but the trees grow rapidly and, like 

 the grasses above mentioned, persist even when the blowout 

 is refilled with sand. The past history and position of the blow- 

 outs are frequently shown by a large Cottonwood or box-elder 

 tree, buried in sand to its lower branches. Two species of Cla- 

 donia soon appear, and are active as soil formers. They are 

 not restricted to the very wettest part, as is Stenophyllus, but 

 extend out upon the naked sand, and also occur in shallower 

 blowouts which have never reached a condition suitable for 

 the sedge. Following the C/<t</<>Hi<i' are Antennaria sp. and He- 

 lianthus oceidentalis, and, a little later, such other species as 

 Hieracium longipilum, Helianthus scaberrimus, Meibomia <:<ih<i- 

 densis, Lacinaria scariosa, Mesadenia atriplicifolia, and others 

 common on the black-soil prairies, and the association is con- 

 verted into prairie scarcely distinguishable, in vegetation at 

 least (PI. XVII.), from the typical prairies of central Illinois. 



A blowout succession is therefore as follows: 



