304 DIVERGENT EVOLUTION THROUGH SEGREGATION. 
clear, but what are the causes of difference of character in the different 
sections, especially when they are exposed to the same environment? 
These causes all come under what I call intensive segregation, which, 
for the sake of saving repetition, will be fully discussed in a separate 
paper. 
(d) Fertilizational segregation. 
Since writing this chapter on environal segregation I have seen 
Francis Galton’s short article on ‘‘ The Origin of Varieties,” published 
in Nature, vol. XXxIv, p. 395, in which he refers to a cause of segrega- 
tion that had not occurred to me. He says: “If insects visited pro- 
miscuously the flowers of a variety and those of the parent stock, then, 
supposing the organs of reproduction and the period of flowering to be 
alike in both and that hybrids between them could be produced by 
artificial cross-fertilization, we should expect to find hybrids in abun- 
dance whenever members of the variety and those of the original stock 
occupied the same or closely contiguous districts. It is hard to account 
for our not doing so, except on the supposition that insects feel repug- 
nance to visiting the plants interchangeably.” 
9. Following the form of nomenclature adopted in this paper, I vent- 
ure to call this principle fertilizational segregation. 
It is evident that segregation of this form depends on divergence of 
character already clearly established, and therefore on some other form 
of segregation that has preceded. It is also segregative rather than 
separative, in that it perpetuates a segregation previously produced, 
which might otherwise be obliterated by the distribution of the differ- 
ent forms in the same district. The form of segregation that precedes 
fertilizational segregation, producing the conditions on which it de- 
pends, must, from the nature of the case, be local segregation. Chronal 
and impregnational segregation, when imperfectly established, might 
be fortified by fertilizational segregation; but, in the case of plants, 
these are all dependent on previous local segregation. 
(e) Artificial segregation. 
Artificial segregation is segregation arising from the relations in 
which the organism stands to the rational environment. As the oper- 
ation of this cause is familiar, and as it was considered in the last chap- 
ter when discussing the effects of segregation, we pass on, simply 
calling attention to the fact that it is a form of environal segregation. 
THE IMPORTANCE OF ENVIRONAL SEGREGATION. 
We must not assume that the various forms of environal segregation 
are of small influence in the formation of species because sexual or 
impregnational incompatibility is a more essential feature, without 
which all other distinctions are liable to be swept away. The impor- 
tance of the forms of segregation discussed in this chapter lies inthe fact 
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