Jennings : A Botanical Survey of Presque Isle. 317 



Each of the above mentioned consocies may occur over a certain 

 area with the facies alone, but over much of the habitat there is more 

 or less of a commingling of the different facies. The Panicum- 

 Artemisia consocies occupies a large part of the southern and middle 

 portion of the habitat, reaching out to the drift-beach in many places 

 towards the south, and being replaced towards Long Ridge very 

 largely by the Andropogon fiircatus consocies. 



In some of the most exposed parts of the habitat, and where the 

 wind has a clear sweep, is to be found the Cladonia consocies. The 

 latter consocies certainly plays a considerable part as a sand-binder 

 and probably prepares the way for colonization by other plants. With 

 the Cladonia is associated Ceratodon purpurcus, occurring mainly as 

 little flat concentric disks, sometimes attaining a diameter of six inches 

 before the central portion dies and the family becomes a community. 

 As a sand-binder the moss must also be of considerable importance, 

 especially when abundant, as in a number of small areas. Each moss 

 disk acts as an obstruction, behind which the sand can be seen col- 

 lecting in a miniature dune."^ 



Principal Species. — The principal species to be noticed in the 

 Panicum-Artemisia formation are Lathyrus viaritimus, Solidago nem- 

 oralis, and Aster ericoides. Lathyrus mai-itimus has a mode of dissem- 

 ination much different from that of the facies mentioned. Its dis- 

 seminules are not readily blown about and promiscuously scattered by 

 the wind, and the structure of the Lathyrus ^.%%oc\z.\\oxi'?> is more prop- 

 erly to be approached from the standpoint of aggregation ; the groups 

 thus being recognized as family, community, or society, according to 

 the extent of the aggregation. 



A few plants stray into the sand-plain habitat from "the drift-beach, 

 such as Xanthium, Cakile and Strophostyles, but they occur only in 

 the part immediately adjoining that habitat, never in the older part 

 of the sand-plain near Long Ridge. 



Secondary Species. — Occurring apparently promiscuously in the 

 consocies mentioned above are the following secondary species : 



Euphorbia polygonifolia, Onagra Oakesiana, 



Onagra biennis, Gnaphalium polycephalutn, 



Cenchrus carolinianus. 



^- Cf. Warming, E. " Lehrbuch der Oekologischen Pflanzengeographie," pp. 

 243-244. 



