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Updated: May 11, 2025
They had analysed soils, estimated the rainfall, and examined the germination of seeds; they understood such mysterious terms as bacteria, protozoa, cotyledons, trenching and ridging, cross-fertilization and spermatozoids, and had some elementary acquaintance with the theory of the rotation of crops.
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.
In consequence, no young individual with an undivided primary leaf was planted out. Choosing the 20 or 30 best specimens in the seed-pan, no further selection was required, and the whole lot could be left to cross-fertilization by insects. The observation of this distinguishing mark in the young seedlings has led to the discovery of another quality as a starting-paint for further selection.
In some flowers this separation is effected, as I have shown, by their maturing at different periods; in others, as in the iris, by mere mechanical means; while in a long list of plants, as in the willow, poplar, hemp, oak, and nettle, the cross-fertilization is absolutely necessitated by the fact of the staminate and stigmatic flowers being either separated on the same stalk or on different plants, the pollen being carried by insects or the wind.
This may best be done by determining the degree of inheritance for the various constituents of the race during a series of years. It is only necessary to apply the two precautions of excluding all cross-fertilization, and of gathering the seeds of each individual separately.
"Now, my friends, the bookseller is one of the keys in that universal adding machine, because he aids in the cross-fertilization of men and books. His delight in his calling doesn't need to be stimulated even by the bright shanks of a Coles Phillips picture.
It is lazy, not having the provident habits of the Working-bees; it aids not in the least, so far as we know, the cross-fertilization of plants one great office in the economy of nature which most bees perform, since it is not a pollen-gatherer, but on the contrary is seemingly a drag and hinderance to the course of nature.
By transplanting them into my garden, I have isolated them and kept them free from cross-fertilization with the ordinary type. Moreover, I have brought them under such conditions as are necessary for the full development of their characters. And last but not least, I have tried to improve this character as far as possible by a very rigid and careful selection.
Professor Gray surmised that the pollen was withdrawn on the insect's head, and it might be so withdrawn, but in other allied orchids of the tribe Arethusæ, however, in which the structure is very similar, the pollen is deposited on the thorax, and such is probably the fact in this species. In either case cross-fertilization would be effected.
The numerous and conclusive demonstrations of Darwin, however, have proved that in the competition for existence such self-fertilized offspring quickly yield before the progeny of cross-fertilization. But the distinctive feature of the orchids lies in the fact that this dependence on the insect is wellnigh universally absolute.
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