Jennings: A Botanical Survey of Presque Isle. 369 



give place to the Cephalanthus. In a few years this area will prob- 

 ably support one of the best examples of the Cephalanthus- Cornus 

 formation to be found anywhere on the peninsula. 



Ridge Pond, as might be expected, being somewhat younger than 

 Cranberry Pond, has the Cephalanthus- Cornus formation less well de- 

 veloped than the latter. In fact most of the vegetation in Ridge 

 Pond corresponding to this formation has a transitional appearance. 

 On the south side of the pond Scirpus and Typha still remain in con- 

 siderable quantities, but Cephalanthus, Iris, Rosa Carolina, Proser- 

 pinaca, etc., are invading the habitat quite abundantly. The Rosa 

 carolifia clings quite closely to the border of the shrub-zone surround- 

 ing this habitat, characterized by Alnus ificana and Cornus amomuin. 

 The corresponding zone on the north side of the pond is fairly typical 

 of the Scirpus- Typha formation, Cephalanthus and Rosa having merely 

 just begun to invade the habitat. 



The Sphagnum- Oxycoccus Formation. 



The successor to the Cladium- Calamagrostis formation under cer- 

 tain conditions is a cranberry bog {Sphagnutn- Oxycoccus formation). 

 Just what the conditions are, which determine whether the wet 

 meadow shall pass into a cranberry bog, or into a Rhus-Alnus thicket, 

 are not known to the writer. Where the shores are wide and low, the 

 accumulation of humus in the saturated, undrained Calamagrostis 

 marsh or wet meadow, may finally bring about edaphic conditions 

 too cold and too acid for the ready ecesis of the shrubs, thus permit- 

 ting the entrance of the Sphagnum- Oxycoccus formation. Whether 

 this may be the true explanation or not, the formation appears not to 

 be a regular stage of the succession, but is rather to be regarded as a 

 formation belonging to a more northern succession, and, like the Fra- 

 garia-Polytrichum formation, to which it may be a succeeding stage, 

 it is to be here regarded as an intercalation. 



The structure of this formation, as exemplified at the eastern end 

 of Cranberry Pond, is as follows : 



Fades. — 



Oxycoccus fnacrocarpus, Sphagnum sp. 



Secondary Species. — 



Iris versicolor, Finns strobus, 



Acer rubrutn, Acer saccharinum 



Alnus incana, Spiraa latifolia, 



