OBSERVATIONS ON FERN HABITATS i114 
The total amount of lime in the several samples of 
soil was found to vary from 1.2 to 10.5%, the average 
being 4.4%. When it is considered that the field soils 
of the same regions contain on the average only 0.8% 
of lime the highly calcareous character of the soils sup- 
porting the growth of this fern is evident. Determina- 
tion of the amounts of water-soluble lime gave a similar 
result, the fern soils yielding 0.08%, the field soils only 
%. 
These data clearly indicate that Camptosorus is a lime- 
loving plant; so the problem resolves itself into account- 
ing for the presence of a soil containing 4 or 5% of total 
lime in the crevices of a rock which may carry only 
traces of this substance. The explanation is not dif- 
ficult to find; the soil supporting the growth of the fern 
Is in most cases a black, powdery material consisting 
chiefly of bits of leaves, stems, ete., in various stages of 
decay, and containing only minor amounts of rock frag- 
ments derived from the adjacent ledges. Such vege- 
table matter contains even in its fresh state 2 or 3% of 
lime; and upon its decomposition organic substances 
are volatilized, resulting in a gradual concentration of 
this lime. Some of this substance may be carried away 
by rain water, but enough remains to render the soil 
eaieareous, and to satisfy the lime-requirement of the 
ern. 
In addition to Camptosorus several other rock ferns 
have been studied from the same viewpoint, with similar 
Tesults. They comprise: Asplenium ebenoides, A. mon- 
lanum, A, pinnatifidum, A. ruta-muraria, A. tricho- 
Manes; Cheilanthes lanosa, and Pellaea atropurpurea. In 
(rae 
It has been fully treated by Mr. Frederick V. Coville, in “ The sae 
" Jo cad. Sci., Vol. 3, 1913, p. 77; 
So. 
The soils over limestone are in fact often poorer in lime than those 
os Other rocks, owing to the comparatively great solubility of limestone 
Water, a 
