IMPREGNATIONAL SEGREGATION. 163 
GENERAL OBSERVATIONS ON GERMINAL AND FLORAL SEGREGATION. 
A fact of great importance in its bearing on the origin of varieties 
_ should be here noted. Any variation, arising as a so-called sport, in 
any group of plants where either of these principles is acting strongly, 
will be restrained from crossing, and will be preserved except in so far 
as reversion takes place. Now, there isalwaysa possibility that some 
of the segregating branches of descent will not revert, and that, 
through the special character which they possess in common, they will 
some time secure the services of some insect that will give them the 
benefit of cross-fertilization with each other without crossing with 
other varieties. The power of attaining new adaptations may be 
favored by self-fertilization occasionally interrupted by interbreeding 
with individuals of another stock; for the latter is favorable as intro- 
ducing vigor and variation, and the former as giving opportunity for 
the accumulation of variations. 
These two methods of propagation are so far removed from those 
found in the majority of species that it may be wise to consider any 
transformation arising under such conditions as belonging to a 
separate department of the process of evolution. Organisms that are 
self-fertilized in all their generations seem to stand in nearer relation 
to species entirely without the power of sexual propagation than to 
species in which cross-fertilization is the usual method of propagation. 
(b) IMPREGNATIONAL SEGREGATION. 
Impregnational segregationis due to the different relations in which 
the descendants of one original stock stand to each other in regard 
to the possibility of their producing fertile, vigorous, and fully adapted 
offspring when they consort together. 
In order that impregnational segregation should be established and 
perpetuated, it is necessary, first, that variation should arise, from 
which it results that those of one kind are capable of producing vig- 
orous, adapted, and fertile offspring in greater numbers when breeding 
with each other than when breeding with other kinds; second, that 
mutually compatible forms should beso brought together as to insure 
propagation through a series of generations. In order to secure this 
second condition, it is necessary that, in the case of plants, there 
should be some degree of local, germinal, or floral segregation, and, in 
the case of animals that pair, either pronounced local segregation or 
partial local segregation, supplemented by social or sexual segregation. 
The action of the different forms of impregnational segregation I call 
negative segregation, for they rest on incompatibilities interfering with 
mixed unions or allowing of no offspring, or of but few or inferior 
offspring, as the result of mixed unions, and, unaided by positive seg- 
