396 Annals of the Carnegie Museum. 



however, a considerable number of Querais vebitina trees now in evi- 

 dence, mostly small as yet, so that the habitat will in the not distant 

 future pass into the Qiierciis velutina forest formation, and thus be 

 restored to its proper position with respect to the adjacent normal 

 successions. 



The Pasture Succession. 



The pasture succession (cultural succession) is due, indirectly, to 

 human agency by the pasturing of cattle near the U. S. Life Saving 

 Station (see map). The continual trampling of the normal vegeta- 

 tion into the sand has resulted in the addition of humus to the soil, 

 thus enriching it, and at the same time has made the soil more com- 

 pact, with a greater and more uniform water-holding power, furnish- 

 ing thus suitable edaphic conditions for the invasion of certain ruderal 

 plants, common to such situations, as well as for certain mesophytic 

 grasses, which under constant grazing have formed in places a com- 

 pact and vigorous turf 



The structure of this formation as here presented is as follows : 



Fades. — 



Poa pratensis. 



Secondary Species. — 



Poa t7-iflora, Poa cotnpressa, 



Salix nigra, Trifolium repens, 



Trifolium pratense, Ranunculus abortivus, 



Plantago tnajor, Plantago lanceolatus, 



Cyperus rivularis, Cerastiwn vulgatum, 



Moehringia lateriflora , ■ Me die ago hipuii?ta, 



Onagra biennis, Taraxacum taraxacum, 



Erigeron philadelphicus, Carduus arvensis, 



AcJiillca millefolium. 



The total area occupied by this formation is small, and at one- 

 fourth of a mile from the Life Saving Station it has disappeared 

 entirely. None of the species could be regarded as important enough 

 to merit the rank of principal species, being much scattered and very 

 few in number of individuals. 



Phvtogeographic Relationships of the Flora of Presque Isle. 



The phytogeographic relationships of the flora of Presque Isle are 

 comparatively rather complex. The vegetation of the mainland about 



