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been no intervening prairie stage, the subsoil in which the oaks are 

 rooted is distinctly humic in nature. The secondary species, how- 

 ever, consist of both prairie and sand plants, some of the latter of 

 which, as Junciis balticus liftoralis, may have persisted through the 

 prairie stage. The same thing happens with respect to the heath. As 

 soon as the oak becomes dominant, by its foliage, light is cut off from 

 the heath plants, and consequently the heath is gradually replaced. 

 With the disappearance of the heath plants the sand is left exposed to 

 blowing. In such situations blowouts are very common. The in- 

 vasion of the pines takes place much slower because that necessitates 

 the dying of the old pine trees. The oaks can not drive these out as 

 they can the her]:)aceous vegetation. The young pines can not germi- 

 nate or develop under the shade of the oaks, which results in the ex- 

 tinction of the pines by the dying of the old trees. As soon as a pine 

 dies, young oaks spring up in its place. They could not do this be- 

 fore on account of the great shade from the pine. Once sufficient 

 light is allowed, the oaks very rapidly replace the spot with trees, 

 against which invasion, in this region, the pines can do nothing, 



The Liatris scariosa association may develop contemporaneously 

 with the Quercus velniina, but usually Liatris scariosa develops first, 

 and as it is a fairly open association the Quercus veliitina quite read- 

 ily invades it. It retains nearly all of its identity, however, even after 

 invasion, because there is not as yet sufficient food material to support 

 a dense growth of oak. As soon as the oak does become dense, the 

 Liatris scariosa gives way. 



In its primary stages the Quercus velutina association occupies 

 stable sandy soil where humification is the rule. The humus, however, 

 is not abundant, and consequently a luxuriant undergrowth is not de- 

 veloped. Protection against wind and sun is afforded, resulting in a 

 flora somewhat mesophytic in tendency, but the succession of this 

 association to a distinctly mesophytic one requires a space of very 

 many years. In the mature stages of the development of this asbo- 

 ciation humification is very slow and may be absent. The oaks them- 

 selves are well developed but their shade keeps out sand plants which 

 would make a dense ground covering, while there is not sufficient 

 food material in the soil to permit the growth of mesophytic forms 

 which require the amount of shade that the oaks furnish. For these 

 reasons eremacausis again takes hold and very materially increases 

 the length of time between this association and the one that will 

 finally succeed it. 



Because of its great diversity of environments this association has 

 a large number of secondary species, many of which belong more 

 properly to the associations which the black oak has displaced. The 



