614 Validity of the Doctrine of Mutation. 
useless, although if applied to the pistil, it is capable of 
producing an abundance of good seed. It is evident 
that this condition cannot have arisen either by gradual 
modifications or under the influence of the ordinary se- 
lection of useful characters. 
All the difficulties which we have mentioned as be- 
setting the current view, disappear if we substitute muta- 
bility for fluctuating variability, as the source of the 
origin of species ; and there is no doubt that adaptations 
can be explained by mutability just as satisfactorily as 
by fluctuating variability. 
8. VEGETATIVE MUTATIONS. 
In order to conduct an experimental investigation 
into the manner in which mutations arise, it is necessary 
to know when they occur. According to the prevailing 
opinion this moment is assumed to be that of fertilization. 
GALLESIO clearly expressed this view at the beginning 
of the last century, and advocated it against the belief 
in the direct influence of the environment which was 
common amongst breeders at that time. 1 Some associa- 
tion of species-forming variability with fertilization is 
generally regarded as being clearly demonstrated both 
in the animal and vegetable kingdoms, and especially for 
annual plants and those which are ordinarily multiplied 
by seed. 
On the other hand we have the bud variations, or 
vegetative mutations as they should rather be called. They 
were well known to the older scientists, but DARWIN was 
the first to insist on their importance by collecting all 
1 G. GALLESTO, Traitc dn Citrus; Tcorici dclla riproduzione rcgc- 
tabile, Pisa, 1816; DE CANPOLT.E, Physiologic regctalc, IT. p. 720. 
