418 BOTANICAL GAZETTE [DECEMBER 
they are thinner, with more acute pinnae. To what extent P. Scouleri 
represents the direct action of the environment, and to what extent 
it has developed into a really independent species can only be deter- 
mined finally by experiment, but certainly it is very variable, and is 
also profoundly modified by the environment. Its variability is evi- 
dence on the point demonstrated by the oaks and shrubs. 
A most remarkable monstrosity, many individuals of which have 
lost all characteristics of P. calijornicum and are indistinguishable 
from a freak of P. vulgare reported from Germany, was first found 
near Chico, where it had complete possession of a small patch of 
ground (jig. 9). Its essential feature is that the distal part of the 
midrib of the lateral pinnae and segments, and the whole axis of 
the terminal one, develop no wing, but spring free from the spore- 
bearing surface of the blade. In correlation with this, the growth 
of the segments is arrested, making their apices round and dentate, 
and the frond as a whole truncate-oblanceolate. The free part of 
the midrib may be prolonged to at least the natural length of the 
segment; or may be shorter, even to the extent of not springing free 
at all; in which case the development of the blade may be anywhere 
from very stunted to normal. All the pinnae may be affected; or 
some of them toward the apex may not; or only a few or a single one 
may be modified, making a complete series from normal fronds to 
the most monstrous. Since collecting it near Chico, I have twice 
found a few ferns like these back of Palo Alto, but in these only a part 
of the segments were ever malformed. 
Il. 
I wish now to use this material, both the shrubs and the ferns, 
as the basis for a discussion of the “mutation theory” in bionomics 
It is already clear enough that I do not believe there is any foundation 
at all for the view that mutations as essentially distinct from ordinary 
variations exist. That they do not I endeavor to show. But the 
mutation theory under one or another caption has for years — . 
refuge for those who on any ground regarded natural selection 45 
inadequate to the demands upon it, and has recently been s0 poe 
fully supported by Dr Vries and others (BATESON, WETISTEIN; 
etc.), and has been so enthusiastically received that it has become 
