286 OHIO BIOLOGICAL SURVEY 



nor running far onto their perpendicular faces. In other regions this 

 same species is found in habitats that seem to an American botanist 

 almost unbelievable. Warming' mentions it as occurring on gray sand 

 dunes in Europe. Such habitats are entirely inexplicable on the hy- 

 pothesis of a preference of Polypodium for any one of them, but are 

 entirely consistent with the view that this species has been crowded 

 out of the more favorable habitats and must grow where it can. 



Doubtless there are crevice plants which have decided preferences 

 for their habitats, and indeed some such occur in the present region, 

 but the writer has been surprised to find that such other rock-dwelling 

 ferns as Camptosorus rhizophyllus, Asplenmm trichomanes, and As- 

 plenium montanum grow thriftily in an ordinary garden bed. One 

 inay observe the same thing over and. over again if he will read in 

 the catalog of such a florist as Edward W. Gillett, who makes a specialty 

 of cultivating the native plants, the directions given for managing 

 various plants. One finds there that all of the cliff: ferns succeed well 

 if grown in a bed with good drainage, including, besides those men- 

 tioned above: Pellaea atropurpurea, Cheilanfhes gracilis, Polypodium 

 vulgar e '("which will adapt itself to almost any kind of soil not too 

 wet") and Woodsia illevensis. Similar directions are also given for 

 such chasmophytes as Campanula roiuudifolia. 



Sullivantia Cliffs. Wherever, under a waterfall or elsewhere, water 

 trickles slowly down over an overhanging clifit' sufficiently well ilhimi- 

 nated, Sullivantia is apt to occur. It seems not to thrive except where 

 its roots are kept constantly wet. In such situations it sometimes almost 

 covers the face of the rock with its beautiful glossy foliage. Sullivantia 

 is one of the plants which must certainly be classed as preferring the 

 rock to all other habitats. It is never found far away from the clifPs, 

 and though by far tlie larger proportion of its seeds must drop down 

 on to the ground below the cliff, it only is rarely that one finds it 

 growing there (fig. 21). 



Isolated Boulders. The structure of the sandstone is such that 

 along every ravine the cliffs are lined with large boulders which have 

 cracked off and gradually slumped away down the slope. For the 

 most part these rocks are occupied by societies occurring in other situa- 

 tions and already described, such as the shade-loving herbage of the 

 forest floor or the huckleberry brush of the cliff top, according to the 

 conditions prevailing on the particular rock. But there is at least one 

 societv which reaches its best development only on such boulders. 



2. Ecology, p. 267. 



