BENEDICT: NEW VARIETIES OF NEPHROLEPIS 229 
With respect to the present group of horticulturally produced 
forms, it appears evident that the lack of adaptability to natural 
conditions shown by most of them would prevent their establish- 
ment if they were to be introduced. This statement is probably 
true for the original sports of var. bostoniensis as well as for the forms 
of later vegetative generations, and this fact in itself is an adequate 
explanation of the non-occurrence of any of these forms wild. 
On this assumption they represent new forms produced in the 
course of evolution, most of which would be eliminated by the 
discriminating agency of natural selection. They differ therefore 
from wild forms showing the same types of variation, only in their 
non-adaptability. Certainly the three lines of variation along 
which these forms of Nephrolepis have been differentiated, and 
especially the lines of increase in division and dwarfing, can be 
paralleled by similar lines of variation among wild forms which 
have succeeded better because provided with the means to meet 
natural conditions of competition, etc. Certainly also the forms 
described in this paper comprise, within their extremes of variation, 
greater differences than are required for the differentiation for 
many natural species. For example, differentiation of species 
and even genera on the basis of leaf division is too common, not 
only among ferns but also among flowering plants, to require 
more than mention. 
As possible corollaries to the statements of the preceding para- 
graphs, two points are of interest and may be indicated in the form 
of questions. Is the rapidity of evolution of these Nephrolepis 
varieties, fifty or more in fifteen years, any indication of the speed 
of evolution of wild forms of similar distinctiveness? Or does the 
fact, that nearly all if not all of these forms would lose out in the 
struggle for existence, indicate that, while the appearance of ill- 
adapted variations may be common, the appearance of successful 
Variations is most uncommon? 
In the preceding paragraphs it has been assumed that the 
variations of these cultivated ferns are homologous with similar 
variations occurring among wild species. If this is true, (that the 
two lines of variations are homologous) it is not improbable that the 
causes may be similar. These causes may be sought by experi- 
mental methods, by the cultivation of a variety which shows a 
