wherry: the habitat of the walking fern 673 



were growing were collected at some twenty places in Pennsyl- 

 vania, Maryland, Virginia, and West Virginia. It is a pleasure 

 to acknowledge the assistance in locating these stations received 

 from Mr. Harold W. Pretz, of Allentown, Pa., Prof. Glenn V. 

 Brown and Prof. N. F. Davis of Bucknell University, Lewisburg, 

 Pa., and Dr. T. C. Stotler and Prof. H. T. McDonald, of Harpers 

 Ferry, W. Va. 



The walking fern was found not only on limestone, but also 

 on various rocks not ordinarily classed as calcareous, comprising 

 granite, schist, shale, sandstone, and quartzite, as well as on 

 tree trunks, both living and dead. To make certain that these 

 rocks were actually low in lime, analyses were made on samples 

 collected as near as possible to the roots of the fern plants. 

 Standard methods of analysis were employed, involving de- 

 composition of the rock by evaporation with hydrofluoric acid 

 or by fusion with sodium carbonate, removal of the iron and 

 aluminium by ammonium hydroxide, and precipitation of the 

 calcium as oxalate, followed by ignition and weighing as lime. 

 For completeness, several undoubtedly calcareous rocks were 

 also analyzed, being first dissolved in hydrochloric acid and the 

 lime separated as above outlined. The several rocks were found 

 to vary in lime content from 53.8 per cent down to less than 

 0.1 per cent; details are given in Table 1, below. 



At the outset, then, it was apparent that the walking fern 

 could not be depended on as an index of calcareous rocks. From 

 a theoretical viewpoint, however, plants would be expected to 

 respond not so much to the rock upon which they grow as to 

 the soil which clothes that rock, since it is from the soil that 

 their mineral nutriment is directly obtained. Analysis showing 

 from 30 to 40 per cent of lime in the ash of the plant, it was 

 decided to extend the investigation so as to determine whether 

 the walking fern might perhaps be limited to highly calcareous 

 soils. 



That the soil supporting plant growth is not necessarily 

 closely related in composition to the underlying rock has been 

 repeatedly pointed out, 2 yet is not always recognized in studies 



2 Compare, Coville, Frederick V. The formation of leafmold. Journ. 

 Wash. Acad. Sci., 3: 77. 1913; Ann. Rept. Smithsonian Inst., 1913, 333. 1914. 



