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Not until the time of Christian Conrad Sprengel (1735) did this and other similar riddles begin to be cleared up, that distinguished observer having been the first to discover in the honey-sipping insect the key to the omnipresent mystery. Many flowers, he discovered, were so constructed or so planned that their pollen could not reach their own stigmas, as previously believed. The insect, according to Sprengel, enjoyed the anomalous distinction of having been called in, in the emergency, to fulfil this apparent default in the plain intentions of nature, as shown in the flower. Attracted by the color and fragrance of the blossom, with their implied invitation to the assured feast of nectar, the insect visited the flower, and thus became dusted with the pollen, and in creeping or flying out from it conveyed the fecundating grains to the receptive 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.

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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 in the struggle of their immediate surroundings, and inheriting the peculiarity of their parent, showed flowers possessing the same cross-fertilizing device. The seeds from these, again scattering, continued the unequal struggle in a larger and larger field and in increasing numbers, continually crowding out all their less vigorous competitors of the same species, at length to become entire masters of the field and the only representatives left to perpetuate the line of descent.

Thus we find in almost every flower we meet some astonishing development by which this cross-fertilization is effected, by which the transferrence of the pollen from one flower to the stigma of another is assured, largely through the agency of insects, frequently by the wind and water, occasionally by birds. In many cases this is assured by the pollen-bearing flowers and stigmatic flowers being entirely distinct, as in cucumbers and Indian-corn; perhaps on different plants, as in the palms and willows; again by the pollen maturing and disseminating before the stigma is mature, as already mentioned, and vice versa.

From these, the simplest forms, we pass on to more and more complicated conditions, anomalies of form and structure-devices, mechanisms, that are past belief did we not observe them in actuality with our own eyes, as well as the absolutely convincing demonstration of the intention embodied: exploding flowers, shooting flowers, flower-traps, stamen embraces, pollen showers, pollen plasters, pollen necklaces, and floral pyrotechnics-all demonstrations in the floral etiquette of welcome and au revoir to insects.