290 



OHIO BIOLOGICAL SUEVEY 



which follows back into the cave as far as its particular light require- 

 ment will permit. A considerable number of species are frequently 

 found in such habitats, but most of them must be classed as accidental. 

 Among the few which seem to have a somewhat definite place in such 



Fig. 24. .\ Wet Cave Occupied by Fei'ns (Dryopteris margrinale & D. spinulosum) as far back 



as the Illumination Permits. Beyond them a Zone of Lichens. In the Foreground 



a Dead Cane of Sambucus racemosus. 



habitats only three need be mentioned: SmnbHcus racnnosa, the red 

 elderberry, is oftentimes to be found only in such habitats, being appar- 

 ently crowded out of other habitats. Dryopteris marginalis and D. 

 spinulosa are, however, the most conspicuous and constant inhabitants 

 of the wet caves. They follow far back into the weak light where, 

 undisturbed by other vegetation, they form very beautiful and perfect 

 rosettes, conspicuously oriented, of course, toward the source of light 

 (fig. 24). Beyond the reach of any vascular plant is a zone of crustose 

 lichens which covers the surface of the rock fragments. 



THE GUILD OF SHADE-LOYIXG EVERGREEN HERBS 



Most abundant on shaded rocks, tho often found in other 

 habitats, especially in the upland forest, is a guild of plants which 

 requires separate consideration. These are the prostrate or aeaulescent 

 herbs with evergreen or hibernating leaves. They share the advantages 



