52 AMERICAN FERN JOURNAL 
into related but physiologically distinct species in six 
generations. But some authorities on European ferns 
question the distinctness of the species concerned; more- 
over, it was possible to produce the alleged change in 
one direction only; and finally, the supposed physiolo- 
gical distinctness was not a matter of favoring acid on 
one hand and calcareous matter on the other, but toler- 
ance to presumably high magnesium content of soil de- 
rived from serpentine rock, as contrasted with low mag- 
nesium content typified by ordinary garden soils. 
In this connection it may be pointed out that in the 
case of Asplenvwm ebenoides, which is regarded by most 
authorities as a recent hybrid between Camptosorus and 
Asplenium platyneuron,—a view that has been confirmed 
experimentally—the hybrid does not deviate essentially 
in soil requirement or tolerance from its parents. The 
same is evidently true of Asplenrum gravesii, also a 
present-day hybrid. It therefore appears that in the 
pairs or groups of related species above shown to ex- 
hibit contrasts in soil reaction, the greater the divergence 
in reaction, the longer time has been required for their 
development since the original separation. In the three 
most strongly marked cases, namely Camptosorus and 
Asplenium pinnatifidum, Asplenium montanum and A. 
Ruta-muraria, and the small Woodsias, it would be 
inferred that the separation occurred at some fairly 
remote geological time. 
It may be urged, then, in concluding this paper, that 
in future discussions of relationships between such re- 
action-sensitive plants as these rock ferns it will be 
well worth while to pay some attention to the soil re- 
actions. 
Wasuineton, D. C, 
