Jennings : A Botanical Survey of Presque Isle. 331 



{d) Sorghastrum nutans Consocies, 

 (^) Cladonia Consocies, 

 (y) Polytrichuin Consocies. 



Most of the above consocies may appear pure, and over consider- 

 able areas may consist of the facies alone, but usually several of the 

 facies are promiscuously scattered about, forming a mixed open struc- 

 ture. The Panicum-Arteniisia consocies occupies more generally the 

 open, more exposed positions nearer the lake, while in the most ex- 

 posed of the more inland parts of the habitat occurs the Cladonia 

 consocies. Areas apparently lowered nearer to the water-table by the 

 drifting away of the sand ("fossil beaches," or "blow-outs") are 

 usually occupied by either the Stenophyllus capUhvis consocies, the 

 Sorghastrwn nutans consocies, or by the Polytrichum consocies, the 

 different consocies being commingled or occurring alone. Polytrichum 

 sometimes forms a pure carpet, and, where occurring with Sfenophyllus, 

 often crowds out that species altogether, bringing on the final appear- 

 ance of a heath. The formation of humus with either Stenophyllus or 

 Polytrichum is quite rapid, the organic matter and indrifting sand 

 being bound firmly together by the roots and rhizoids. Inland, 

 towards Long Ridge, the Andropogon furcatus consocies becomes more 

 and more abundant, usually replacing the Panicum-Artemisia consocies 

 altogether as the forest is approached. 



Principal Species of the Panicum-Artemisia Formation. — 

 Lathyrus maritimus, Aster ericoides, 



Solidago ne mora lis, Arabis lyrata. 



In the smaller areas of the sand-plain between the lagoons and 

 marshes near the southern end of the extension of Long Ridge and 

 northwest of Horse-Shoe Pond the force of the winds is much broken 

 by the quite abundant thickets and cottonwood trees, and in these 

 sheltered positions occurs the Arabis lyrata society, which determines 

 thus a vernal aspect, being usually in full bloom on May 15 (see 

 Plate XXXIV). Associated with Arabis as secondary species are 

 Moehringia lateriflora and Arenaria serpyllifolia. During the period 

 of bloom oi Arabis the society is quite conspicuous, appearing during 

 that aspect as a prominent part of the formation. 



The Lathyrus maritimus society occurs mainly in the new soil a 

 short distance back from the drift-beach and usually more or less in 



