ive stigma, which they could not otherwise reach.
Such was Sprengel's belief, which he endeavored to substantiate in an
exhaustive volume containing the result of his observations pursuant to
this theory.

But Sprengel had divined but half the truth. The insect _was necessary_,
it was true, but the Sprengel idea was concerned only with the
_individual_ flower, and the great botanist was soon perplexed and
confounded by an opposing array of facts which completely destroyed the
authority of his work--facts which showed conclusively that the insect
could _not_ thus convey the pollen as described, because the stigma in
the flower was either not yet ready to receive it--perhaps tightly
closed against it--or was past its receptive period, even decidedly
withered.

[Illustration]

This radical assumption of fertilization in the individual flower, which
lay at the base of Sprengel's theory, thus so completely exposed as
false, discredited his entire work. The good was condemned with the bad,
and the noble volume was lost in comparative oblivion--only to be
finally resurrected and its full value and significance revealed by the
keen scientific insight of Darwin (1859). From the new stand-point of
evolution through natural selection the _facts_ in Sprengel's work took
on a most important significance. Darwin now reaffirmed the Sprengel
theory so far as the necessity of the insect was concerned, but showed
that all those perplexing floral conditions which had disproved
Sprengel's assumption, instead of having for their object the conveying
of pollen to the stigma of the _same_ flower, implied its _transfer_ to
the stigma of _another_, cross-fertilization being the evident design,
or evolved and perpetuated advantage.

This solution was made logical and tenable only on the assumption that
such evolved conditions, insuring cross-fertilization, were of distinct
advantage to the flower in the competitive struggle for existence, and
that all cross-fertilized flowers were thus the final result of natural
selection.

The early ancestors of this flower were self-fertilized; a chance
seedling at length, among other continual variations, showed the
singular variation of ripening its stigma in advance of its pollen--or
other condition insuring cross-fertilization--thus acquiring a strain of
fresh vigor. The seedlings of this flower, coming now into competition
with the existing weaker self-fertilized forms, by the increased vigor
won