Sort REacTIONS OF CERTAIN FERNS—II 51 
atropurpurea, is much more tolerant of acid conditions 
than the other. Camptosorus rhizophyllus and Asplen- 
ium pinnatifidum, which seem to the writer to be more 
closely related than the usual nomenclature would sug- 
gest, because of their convergence in such characters as 
structure of the cells in their stipes and scales, rooting 
at the frond-tips, and even netted arrangement of veins,* 
as well as the ‘ability of the former to hybridize with at 
least one species of Asplenium—are even more strik- 
ingly different in soil preference. The former is a cal- 
eareous soil plant, somewhat tolerant of acidity; the 
latter, an acid soil plant, only slightly tolerant of calcium. 
Asplenium Bradleyi is essentially identical in soil re- 
quirements with A. montanum, both being acid soil plants 
intolerant of calcium; but the relative of the latter, A. 
Ruta-muraria, differs radically in this respect, being an 
alkaline soil plant, almost intolerant of acidity. Poly- 
podium vulgare and P. polypodioides also differ in their 
ultimate soil preference, although overlapping consider- 
ably in range of tolerance. Woodsia glabella is a cal- 
careous soil species intolerant of much acidity, while 
the related W. Ilvensis is an acid soil plant not very 
tolerant of caleareous matter. It is interesting to note 
that W. alpina, which is intermediate between these in 
morphologic characters, is also intermediate in its pref- 
erence to soil reaction. Finally, Filix bulbifera and F. 
fragilis, while alike in being calcareous soil plants, differ 
distinetly in tolerance for acid, the latter showing the 
greater. 
Adaptation to contrasted soil reactions, with the phy- 
siological divergence it implies, seems to the writer 
likely to have required a long period of evolution. It is 
true that in a research frequently cited, Sadebeck® be- 
lieved that he had produced a change of two Aspleniums 
s’Waters, C. E. Fern Bull., 10, 2, 1902. 
*Ber. Sitz. Ges. Bot. Hamburg, 3, 4, 1887. 
