366 Evolution and Adaptation 
NuMBER NuMBER AVERAGE AVERAGE 
No. or SEEDS 
NATuRE oF UNION oF FLowers | oF Capsuves | No. oF SEEDS eek POWER: 
FERTILIZED Propucep | PER CAPSULE Rennnset 
The 6 legitimate unions 75 56 96.29 71.89 
The 12 illegitimate unions 146 36 44.72 11.03 
This table shows that the fertility of the legitimate to that 
of the illegitimate is as 100 to 33, as judged by the flowers 
that produced capsules ; and as 100 to 46 as judged by the 
average number of seeds per capsule. It is evident, there- 
fore, that “it is only the pollen from the longest stamens 
that can fully fertilize the longest pistil; only that from the 
mid-length stamens, the mid-length pistil; and only that 
from the shortest stamens, the shortest pistil.” 
Darwin tries to connect this fact with the visits of insects 
to the flowers. He says: ‘‘And now we can comprehend 
the meaning of the almost exact correspondence in length 
between the pistil in each form and of a set of six stamens 
in two of the other forms; for the stigma of each form is 
thus rubbed against that part of the insect’s body which be- 
comes charged with the proper pollen.” A further conclusion 
that Darwin draws is “that the greater the inequality in 
length between the pistil and the set of stamens, the pollen 
of which is employed for its fertilization, by so much is the 
sterility the more increased.” Darwin also makes the fol- 
lowing significant comment on the problem here involved: 
“The correspondence in length between the pistil in each 
form, and a set of stamens in the other two forms, is prob- 
ably the direct result of adaptation, as it is of the highest 
service to the species by leading to full and legitimate fer- 
tilization.”” He points out, on the other hand, that the in- 
creased sterility of the illegitimate unions, in proportion to 
the inequality in length between the pistil and the stamens 
