334 DIVERGENT EVOLUTION THROUGH SEGREGATION. 
that has many members, but as it does not directly produce the nega- 
tive segregation which is, in such cases, the necessary antecedent of 
permanent divergence, we can not, in accordance with the usage of lan- 
guage, call it the cause of the permanent divergence. Moreover, though 
it may be in accordance with ordinary language to call the negative 
segregation, which is the immediate antecedent of the permanent diver- 
gence, the cause of the same, it will be more correct to call the coin- 
cidence of the negative and positive segregations the cause, and still 
more accurate to say that the whole range of vital activities (when sub-— 
jected to the limitations of any sexual incompatibility that corresponds 
in the groups it separates to some previous but ineffectual local, germi- 
nal, or floral segregation) will produce permanent divergence. 
In many cases not only is the entrance of impregnational segrega- 
tion the cause of the commencement of permanent divergence, but its 
continuance is the cause of the continuance of the divergence. The 
clearest illustration of this is found in the case of plants that are fer- 
tilized by pollen that is distributed by the wind. All the higher, as 
well as the lower, groups of such plants would rapidly coalesce if each 
erain of pollen was capable of producing fertilization, with equal cer- 
tainty, promptness, and efficiency, on whatever stigma it might fall. 
We may also be sure that, with organisms that depend upon water for 
the distribution of their fertilizing elements, impregnational segrega- 
tion is an essential factor in the development of higher as well as of 
lower taxonomic groups. 
It is important to observe that, in the cases under consideration, the 
inferior fertility or vigor resulting from the crossing of the incompatible 
forms is as truly a cause of divergence as the inferior opportunity for 
crossing which from the first existed between the members occupying 
different localities or between the flowers growing on different trees of 
the same species. The former has been called negative, and the latter 
positive, segregation, not for the sake of distinguishing different grades 
of efficiency, but for the sake of indicating the different methods of 
operation in the two classes of segregation. 
c) Institutional segregation. 
Institutional segregation is the reflexive form of rational segrega- 
tion. It is produced by the rational purposes of man embodied in in- 
stitutions that prevent free inter-generation between the different parts 
of the same race. 
As the principal object of the present paper is to call attention to 
the causes of segregation acting independently of effort and contriv- 
ance directed by man to that end, it will be sufficient to enumerate 
some of the more prominent forms under which institutional segrega- 
tion presents itself, noting that some of these influences come in as 
supplemental to the laws of segregation already discussed, simply re- 
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