342 BOTANICAL GAZETTE [ MAY 
presence of the parent species is not a necessity, since fern plants 
are often long-lived, and the greater vigor of the crosses might render 
them resistant to conditions sufficiently adverse to destroy the parent 
species.” While many of the plants studied by BrNEpict and others 
may be hybrids, it would be extremely difficult to distinguish, in such 
cases, between “sports” and “hybrids,” especially when the supposed 
parents are not present, and the conclusions founded on such evi- 
dence must always have a large element of uncertainty. Ferns, 
like other plants, are known to vary widely under different conditions, 
and certain tendencies toward variation are recognized by students 
of this group (31, p. 272). 
The uncertainty of conclusions founded on a study of the sporo- 
phyte is emphasized by the work of SADEBECK (40, 41). This author, 
sowing spores of Asplenium adulterinum and of A. Serpentini on 
a serpentine-free substratum for successive generations, obtained 
respectively Asplenium viride and A. Adiantum nigrum, thus show- 
ing that forms previously described as species were but serpentine 
varieties. The first transformation to the non-serpentine form of 
the species occurred in the former case in the fourth, in the latter 
case in the fifth generation, the serpentine form being maintained 
for several generations on a serpentine-free substratum. Even 
cultures, therefore, unless continued for many generations under 
different conditions, may fail to show the real nature of a supposed 
species. 
In discussions concerning hybridity, much weight is given to the 
point that in the characters in which the specimens differ from the 
“type of the species,’ they approach those of some other species. 
This may be due to hybridization as supposed, or it may be due to 
some other cause. The serpentine form of Asplenium viride (“A. 
adulterinum”) assumes, in many respects, an intermediate form 
between the “typical”? A. viride and A. trichomanes, showing that 
an ecological variety may assume a form approaching that of another 
species, : 
If species were clearly recognizable units with distinc 
and if these units were changeable only by hybridization, we should be 
justified in describing intermediate forms as hybrids. But, consider- 
ing the cases mentioned above and the variation that is know? to 
t limits, 
