37° George E. Nichols, 



in many such habitats ever has been xerophytic, and for this 

 reason it has seemed best to treat it under the head of hydrarch 

 successions. The outstanding feature of such a ravine is the 

 intense mesophytism, commonly verging on hydrophytism, of its 

 vegetation. In the periodically inundated zone along the edge 

 of the stream there is a profuse development of mosses and 

 liverworts, which commonly include, among others, the follow- 

 ing species : 



Conoccphalnm conicum Philonotis fontana 



Plagiochila asplenioides Thuidium delicaUdum 



Sphagnum squarrosum Brachythecium rivulare 



Fissidens adiantoides Hylocomium hrevirostre 



Mnium horniim Climacium dendroides 



Mnium punctatum Catharinaea undulata 



Vascular plants are more or less numerous, particularly 

 toward the upper limit of the flood zone. Here the ferns are 

 represented by a wealth of species, among which Polystichum 

 Braunii is especially characteristic, while the seed plants include 

 some of the most pronounced shade- and moisture-loving 

 mesophytes. A list of some of the more representative ferns 

 and seed plants follows : 



Phegopteris polypodioides Aspidhim spmulosum var. 



Phegopteris Dryopteris Streptopus amplexif alius 



Asplenium Filix-femina Geum macro pJiyllum 



Polystichum acrostichoides Circaea alpina 



Polystichum Braunii Galium kamtschaticum 



Aspidium novehoracense Aster acuniinatus 



Along the larger ravine streams the banks are more exposed 

 to sun and wind than along the smaller ones, and the vegetation 

 tends to be less mesophytic, with shade plants in particular much 

 less prominent. The character of the vegetation between low 

 and high water levels is influenced to a more marked degree by 

 the abrading action of the current in flood time. Even here, 

 however, associations of the sort just described are frequently 

 encountered. 



Cliff association-types. — Many cliffs and steep rock outcrops 

 are kept wet to such a degree with dripping water that their 



