674 wherry: the habitat of the walking fern 



of plant habitats; attention is therefore again called to it here. 

 The soil may contain: (1) less lime than the underlying rock if 

 (a) it originated on a non-calcareous rock, but has been trans- 

 ported to a more calcareous one, or (b) lime has been leached 

 from it by the rain; (2) more lime than the underlying rock if 

 (a) it originated on a calcareous rock, but has been transported 

 to a less calcareous one, or (b) lime has become concentrated 

 in it by long continued decay of vegetable matter. 



To determine which of the above relations holds in the case 

 of the walking fern, samples of the several soils were dried at 

 105°C, so that they could be more easily handled, and shaken 

 from the network of roots. The soils in almost every case were 

 found to be filled with rock fragments of all sizes, so that some 

 arbitrary classification, on the basis of size, into " rock " and " soil" 

 particles was unavoidable. A sieve with 40 meshes to the centi- 

 meter was adopted for this purpose, and the various soils were 

 gently sifted through it, the chips of rock and coarse vegetable 

 matter being thereby removed. The particles passing through 

 this sieve were finely powdered in an agate mortar and used 

 for the analytical work. Two-tenth gram samples of the soils 

 were weighed out into platinum crucibles, and ignited over 

 complete-combustion burners to drive off volatile matter; this 

 varied between 20 and SO per cent in the several soils studied. 

 The residues were then fused with sodium carbonate, and analyzed 

 for total lime in the usual way; the results are given in Table 1. 



The total lime is, however, probably not so important in this 

 connection as the soluble lime, for it is conceivable that even in 

 soils high in total lime only a very minute amount may be 

 present in such a form as to be available to the plants. It was, 

 therefore, decided to test the soils for soluble lime. 



It is, of course, impracticable to determine the amount of 

 lime in the natural soil liquid when dealing with such small 

 quantities of material as are available in this case. An excess 

 of water must be added, so that a volume of liquid sufficient 

 for analysis can be obtained. The complexity of soils is so 

 great, and the factors involved so numerous, that it can not be 

 assumed that the composition of a solution obtained by adding 



