wherry: the habitat of the walking fern 679 



The results in the last five columns, and more particularly the 

 last two, show that some of the soils are alkaline, some neutral, 

 and some acid. The chief sources of the alkalinity are, no 

 doubt, calcium and potassium salts of weak organic acids; of 

 the acidity, these acids in a free state; but the amount of soil 

 available is too limited to permit of isolation or identification 

 of these substances. At any rate it is evident that the walking 

 fern is not especially sensitive to variations in the reaction of the 

 soil. 



Summary. — -It has been shown by chemical analysis that the 

 rocks supporting the growth of walking fern (Camptosorus rhizo- 

 phyllus) are by no means necessarily calcareous, but that the 

 soils in which this fern grows are rather high in both total and 

 soluble lime. Rocks high in lime suffer leaching during soil 

 formation, and those low in this constituent gain it through 

 decay of vegetable matter, the ultimate amount varying widely 

 with the conditions, but averaging about 4 per cent. The 

 above results indicate that the view often held, that the occur- 

 rence of calciphilous plants necessarily indicates the presence of 

 lime in the underlying rock strata, is untenable, except in cases 

 where circumstances preclude the accumulation and decay of 

 vegetable matter, and the resulting accumulation of lime in 

 the soil. 



