270 
REV. J. T. GULICK ON DIVERGENT EVOLUTION 
in tlie case of organisms whose fertilizing elements are distributed 
by wind and water, the qualities that produce these negative 
forms of Segregation are usually accompanied by those that pro- 
duce Prepotential Segregation, which is in an important degree 
positive. But even Prepotential Segregation, when produced by 
mutual incompatibility between a few individuals and a numerous 
parent stock, depends for its continuance and development on 
Local, Germinal, or Ploral Segregation, partially securing the 
intergeneration of the few that are mutually compatible. On 
the one hand, Impregnational Segregation depends on some 
degree of Local, Grerminal, or Floral Segregation which is a con- 
stant feature in most species ; but, on the other hand, not only 
do these initial forms of Positive Segregation fail of producing 
any permanent divergence till associated with Impregnational 
Segregation, but the more effective forms of Positive Segregation, 
such as Industrial, Chronal, Fertilizational, Sexual, and Social 
Segregation, often depend on Impregnational Segregation, inas- 
much as the divergence of endowments which produces these 
depends on Impregnational Segregation. Moreover, in all such 
cases, increasing degrees of diversity in the forms of adaptation, 
and consequently of diversity in the forms of natural selection, 
must also depend upon these negative factors, which in their 
turn depend on the weak, initial forms of Positive Segregation . 
Divergent evolution always depends on some degree of Posi- 
tive Segregation, but not always on Negative Segregation. 
Under Positive Segregation of a rigorous form (as, for example, 
complete Geographical Segregation), considerable divergence may 
result without any sexual incompatibility. Darwin has shown, 
by careful experiments, that Integrate Vigour and Fecundity is 
the relation in which the varieties of one species usually stand to 
each other. This fact does not, however, prove that the more 
strongly divergent forms, called species, which are prevented from 
coalescing by Segregate Vigour and Fecundity, did not acquire 
some degree of this latter character before any permanent diver- 
gence of form was acquired. Their having acquired this segre- 
gating characteristic may be the very reason why their forms are 
now so decidedly different, for without it they would have been 
swallowed up by the incoming waves of intergeneration. Again, 
we must remember that forms only moderately divergent are 
habitually classed as different species if they are separated by 
Segregate Vigour and Fecundity (that is by some degree of 
