678 wherry: the habitat of the walking fern 



metamorphic, and sedimentary rocks. Even though in some 

 cases fairly high in lime, these are not ordinarily classed as cal- 

 careous, their lime being united with silica and other constituents 

 in relatively insoluble form; several, indeed, contain only ex- 

 tremely small amounts of lime. When the total lime contents of 

 the soils are compared to those of the rocks, however, wide diver- 

 gences are shown. The several soils vary in total lime from 1.2 to 

 10.5 per cent, containing hi some cases less and in others more 

 lime than the rocks upon which they occur; in other words, in 

 so far as this one constituent is concerned, the composition of the 

 soil bears no relation whatever to that of the underlying rock. 

 Soil transportation on any considerable scale is virtually ex- 

 cluded; but it is evident that leaching out of lime by the rain 

 and its concentration by accumulation and decay of vegetable 

 matter are both effective processes. Which is dominant depends 

 on circumstances, such as exposure to rain, opportunity for leaves 

 to fall in, etc., but the net result is that in cases where the rock 

 is high in lime the soil usually contains less lime than the rock, 

 whereas with rocks low in lime the reverse is usually true; and 

 the average lime content of the soil is slightly more than 4 per 

 cent. If a calcareous soil is defined as one containing more 

 lime than the average field soil (0.8 per cent or less), then the 

 soils supporting the growth of walking fern are certainly highly 

 calcareous. 



The percentage of soluble lime bears no recognizable relation 

 to that of total lime, but it is also on the average many times 

 as great as the figure for ordinary field soils. The habitat of 

 the walking fern is thus calcareous with reference to both total 

 and soluble lime. It is not claimed that the plant grows in 

 these calcareous soils merely because of the presence of abundant 

 lime; more probably the lime acts indirectly by favoring the 

 accumulation of humus or the growth of beneficial microorgan- 

 isms; no doubt the physical condition of the soils, the amount of 

 moisture, the degree of drainage, etc., have an important bearing 

 on the question also; but as this phase of the subject lies entirely 

 outside of the scope of the present investigation it will not be 

 further discussed. 



