Jennings : A Botanical Survey of Presque Isle. 361 



Hypericum boreale, Hypericum canadense, 



Scirpus cyperinus, Juucus canadensis, 



Eleocharis quadrani^ulata, Pontederia cordata, 



N OS toe sp. 



Muskrats have formed many mounds and run-ways in this area, and 

 in so doing have exposed to view the sand, upon which there has 

 been a return of Eleocharis acicularis and a new invader from the 

 shrub-zone, Salix lucida. 



The Cladium-Calamagrostis Formation. 



This formation is being here invaded very rapidly by the shrub- 

 zone around most of the marsh, the pioneer Myrica clumps (families 

 and communities in many cases) being scattered about here and 

 there in advance of the main shrub-zone. Salix cordata here advances 

 by even longer leaps than does the Myrica, but it does not form such 

 compact clumps. 



The structure of the formation at this stage is as follows : 



Fades. — 



Calamagrosiis canadensis (predominant), 

 Cladiuin mariscoides (inconspicuous). 

 Principal Species. — 



Dryopteris thelypteris, Triadenum virginicum, 



Aster ericoides. 

 Secondary Species. — 



Onoclea sensi bills. 



Where the Cladium-Calamagrostis zone is wider, or where for some 

 reason the shrub-zone advances more slowly, the meadow-formation 

 develops a structure consisting of what may be called the Fragaria 

 virginiana society, which is followed later in the season by the Aster 

 ericoides society, as described under Stage E. The structure of the 

 Fragaria virginiana society is as follows : 



Principal Species. — 



Fragaria virginiana. 

 Secondary Species. — 



Dasystotna virginica, Lactuca canadensis, 



Solidago tietnoralis, Solidago canadensis. 



Aster ericoides, Eupatorium perfoliatum, 



Sorghastrum nutatis, Panicutn virgatum, 



Cladonia sp. 



