330 DIVERGENT EVOLUTION THROUGH SEGREGATION. 
plants 63.2 high, and the seven Colchester-crossed 65.37 high; so that 
there was not much difference between the three sets, the self-fertilized 
plants having a slight advantage. Nor was there any great difference 
when only the plants under 36 inches in height were excluded. Nor 
again when all the plants, however much dwarfed and unhealthy, were 
included. 
‘In this latter case the Colchester-crossed gave the lowest average 
of all; and if these plants had been in any marked manner superior to 
the other two lots, as from my former experience I fully expected they 
would have been, I can not but think that some vestige of such superi- 
ority would have been evident, nothwithstanding the very unhealthy 
condition of most ofthe plants. No advantage, as far as we can judge, 
was derived from inter-crossing two of the grandchildren of Hero, any 
more than when two of the chiidren were crossed. It appears, there- 
fore, that Hero and its descendants have varied from the common type, 
not only in acquiring great power of growth and increased fertility 
when subjected to self-fertilization, but in not profiting from a cross 
with a distinct stock; and this latter fact, if trustworthy, is a unique 
case, as far as I have observed in all my experiments.” * 
Let us now consider fora moment what must be the result when such 
a variation occurs in a wild species subject to the ordinary conditions 
of competition. In the first place, it would gradually prevail over 
other representatives of the same local stock, both by its more vigor- 
ous growth and by its greater fertility, especially in the case of flow- 
ers that failed of securing a cross. And afterwards, when it came into 
competition with the equally adapted variety from which it was par- 
tially protected by segregate vigor, it would neither be driven out 
nor lose its separate existence in a commingled race. It will be 
observed that we have in such a case local, germinal, and floral segre- 
gation, each producing partial effects which are enhanced by the seg- 
regate vigor. In order to bring out the relation of these factors to 
each other, let us assume definite values foreach. Let us suppose that 
3, of. the flowers are self-fertilized, 33, are fertilized with pollen from 
another flower of the same plant, 8, are fertilized with pollen from 
other plants of the same new variety, and ;), are fertilized with pollen 
from the older variety occupying contiguous areas. Therefore the sum 
of the segregating influences, which is called the “ Ratio of pure breed- 
ing,” and is represented by Ri in Table 1, equals ;%; and the “Ratio 
of cross-breeding,” represented by ¢ in all the tables, equals +5. Again, 
let us suppose that the fertility of the pure breeds is the same as that 
of the half-breeds, but that the superior vigor of the former is such that 
any one of the pure seeds has twice as good a chance of germinating, 
growing to maturity, and producing seeds as any one of the crossed 
seeds. The general effect on the final result will in that case be the 
Same as s if the ‘¢ Ratio of increase for the pure unions” (which I eall M) 
*<CCTOSS ana self- eet in the vegetable jeden pp. 50, 61. 
