660 Harshberger: Plant formations of Nockamixon Rocks 



Deciduous Forest Formation. The composition of the vegetation 

 of the ravines is somewhat different from that of the talus slope, 

 indeed, the dominant trees found in the glens are so associated as 

 to form a distinct facies of the formation. As the flora of the 

 ravines differs somewhat in each case, it will be considered with 

 reference to the particular gully in which it occurs. The most 

 characteristic ravine is one which cuts back into the middle por- 

 tion of the cliffs. A stream cascades over precipitous rocks 

 covered with mosses and liverworts, among them Marchantia 

 polymorpha. The tree vegetation is as follows : 



Facies : Tilia aniericana^ Uhmis americana. 



Dominant associated specify : Quernts Primis, Acer Sac- 

 charajn, Ostrya virginiana. 



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Shrubby undergrowth (Niederwuchs) : Taxns canadensis 

 (covering slopes extensively), Hydrangea arborescens^ Physocarpits 

 opulifolius^ Rubiis odoratus^ Celastrus scandens. 



Herbs of forest floor : The soil of the ravine slopes is util- 



Impatiens fulva (/. bifli 



efolhini) 



Jlexicaidis iS. latifolia)^ Eup 



Rock herbs : The characteristic rock flora of these ravines 

 includes Aqnilegia canadensis^ Campanula rotnndifolia^ Arabis 

 lyrata^ Geranium Robertiantim^ Heuchera amencana, Ceraslium 



i^L . Caprifoliuni) 



if o Hum, Saxifraga pennsy 



Polypodi 



s 



imptosortis rhizophylh 

 pus opulifolius. 



The most western ravine is filled with such an association of 

 trees that a new facies may be said to exist. 



Facies : Acer Sacchanun^ Fagits americana^ Tsiiga canadensis. 

 These trees comprise the maple-beach-hemlock facies. 



Associated trees : Here grow in association such dominant 

 trees as Tilia americana^ Betula lenta^ Qnercus Pritms^ Morns 

 rubra, and Acer rubrum. The hemlock, Tsuga canadensis^ is not 

 sufficiently abundant to constitute a formation, but it is mixed with 

 the broad-leaved trees in such proportion as to necessitate its in- 

 clusion in the deciduous forest proper. Associated with these trees 

 as an undergroivth are found Taxus canadensis (abundant), Hydran- 



