THKOUGH CUMULATIVE SEGREGATION. 
229 
septemdecvm being entirely separated from all other broods of the 
same race by being belated a year, may be modified by forms of 
Natural Selection that never arise in these other broods. And 
this may be the case even if a brood observing the ordinary time 
is always associated with it in locality. 
5. Seasonal Segregation is produced whenever the season for 
reproduction in any section of the species is such that it cannot 
interbreed with other sections of the species. It needs no argu- 
ment to show that if, in a species of plant that regularly flowers 
in the Spring, there arises a variety that regularly flowers in the 
autumn, it will be prevented from interbreeding with the typical 
form. The question of chief interest is, under what circum- 
stances are varieties of this kind likely to arise ? Is a casual 
sport of this kind likely to transmit to subsequent generations a 
permanently changed constitution ? If not, how is the new con- 
stitution acquired? One obvious answer is that it may arise 
under some special influence of the environment upon members 
of the species that are geographically or locally segregated from 
the rest of the species. 
But may not the variation in the season of flowering be the 
cause of segregation that will directly tend to produce greater 
variation in that respect in the next generation, and so on till 
the divergence in the constitutional adaptation to season is 
carried to the greatest extreme that is compatible with the en- 
vironment P I believe that it not only may, but must have that 
effect; but we should remember that the average form which 
flowers at the height of the season will so vastly predominate 
over the extreme forms that the latter will be but stragglers in 
comparison. 
In regard to the one point of the season of readiness for pro- 
pagation, this principle is segregative ; but in other respects it is 
simply separative, unless through the principle of correlated 
variation other characters are directly connected with the con- 
stitution that determines the season. It will be observed that 
Seasonal Segregation is produced by a parallel and simultaneous 
change in the constitution of members in one place sufficient to 
propagate the species ; while Cyclical Segregation is produced 
by a simultaneous acceleration or retardation in the development 
of members in one place sufficient to propagate the species with- 
out disturbing the regular action of the constitution under 
ordinary circumstances. 
