DIVERGENT EVOLUTION THROUGH SEGREGATION... 329 
what is far more remarkable, the great-grandchildren, raised by cross- 
ing the grandchildren with a fresh stock, had no advantage over either 
the inter-crossed or the self-fertilized great-grandchildren. It thus 
appears that Hero and its descendants differed in constitution in an 
extraordinary manner from ordinary plants of the same species.” “If 
we look to the (ordinary) plants of the ninth generation in Table x, we 
find that the inter-crossed plants (of the same stock) were in height to 
the self-fertilized as 100 to 79, and in fertility as 100 to 26; whilst the 
Colchester-crossed plants (raised by crossing with a fresh stock) were in 
height to the intercrossed as 100 to 78, and in fertility as 100 to 51.”* 
The Colehester-crossed plants were therefore in height to the self-fer- 
tilized as 1 to 0.78 x 0.79, or as 1000 to 616, and ia fertility as 1 to 
0.51 x 0.26, or as 1000 to 133; while the self-fertilized descendants of 
Hero when crossed with the same fresh stock not only had no advan- 
tage over those that had been continuously self-fertilized for nine gen- 
erations, but, as the details of the experiment show, the advantage was 
on the side of the plants raised from the self-fertilized seed. The ex- 
periment was conducted under conditions decidedly unfavorable for the 
production of healthy plants; but as it is usually found that the superi- 
ority of crosses between varieties is most clearly brought to light when 
the competitors are subjected to unfavorable circumstances, it seems to 
furnish even stronger evidence of segregate vigor being occasionally 
produced in the earliest stages of divergent evolution than would have 
been furnished if the same degree of superiority in the self-fertilized 
plants had been obtained under a less severe test. As the case is of 
unusual interest, I give the details as recorded by Darwin: 
“Several flowerson the self-fertilized grandchildren of Hero in Table 
XVI were fertilized with pollen from the same flower; and the seedlings 
raised from them (great-grandchildren of Hero) formed the ninth self 
fertilized generation. Several other flowers were crossed with pollen 
from another grandchild, so that they may be considered as the off- 
spring of brothers and sisters, and the seedlings thus raised may be 
-alled the inter-crossed great-grandchildren. And lastly other flowers 
were fertilized with pollen from a distinct stock, and the seedlings thus 
raised may be called the Colchester-crossed great-grandchildren. In 
my anxiety to see what the result would be I unfortunately planted 
the three lots of seeds (after they had germinated on sand) in the hot- 
house in the middle of winter, and in consequence of this the seedlings 
(twenty in number of each kind) became very unhealthy, some growing 
only a few inches in height, and very few to their proper height. The 
result therefore can not be fully trusted; and it would be useless to 
give the measurements in detail. In order to strike as fair an aver- 
age as possible I first excluded all the plants under 50 inches in height, 
thus rejecting all the most unhealthy plants. The six self-fertilized 
thus left were on an average 66.86 inches high, the eight inter-crossed 
* “Cross and Self-Fertilization,” pp. 47, 60, 61. 
