388 Annals of the Carnegie Museum. 



mulated by the Fhragmites-Typha formation, is almost exclusively 

 humus, and the Cladimn, although usually in evidence in the earlier 

 part of the formation, is relatively unimportant in it. Along the 

 eastern border of Y there is now some Cladium and in the central 

 portion and towards the outlet in the more moist spots there still 

 remain some Phragmites and Typha. 



There is in this formation an early autumn aspect determined by 

 the Aster ericoides society, but occupying rather restricted areas. 

 During late summer a quite conspicuous aspect is determined along 

 the northern side of the meadow by the Parnassia-Gentiana society, 

 this being the only station for this society on the peninsula. 



The Rhus-AImis Formation. * 



The wet meadow, Cladium- Calamagi'ostis formation, is being every- 

 where invaded by a shrub-formation similar to that around the ponds 

 and lagoons described as the RIuis-Alnus formation, but differing 

 somewhat in composition, owing probably to differences in the 

 environment. The structure of the formation here is typically as 

 follows : 



Fades. — 



Rhus typliiim., Alnus incana. 



Principal Species. — 



Solidago canadensis Cornus amomuni. 



Secondary Species. — 



Fragaria virginiana, Alyrica caroliniana, 



Argentina anserina, Vitis vulpina, 



Salix discolor, Salix cordata, 



Toxicodendron piihescens, Rubus sp . , 

 Meibomia dillenii. 



There is here again the larger percentage of humus in the soil, 

 Avhich may be more or less directly the reason for the difference in 

 the composition of the formation. Rhus typhina although present is 

 not abundant, and the thicket is chiefly composed of the Alnus incana 

 consocies. 



The formation presents some alternation. The wet meadow is 

 invaded by Myrica and Cornus amomum, these species, together with 

 some young Alnus, forming an advance zone containing most of the 

 secondary species. This zone is gradually subjugated by the Alnus 

 consocies. 



