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Updated: June 6, 2025
In this respect the historic dates, as collected by Korshinsky, are not very convincing. Vicinism has of course, almost never been excluded, and part of the multiformity of the offspring must obviously be due to this most universal agency. Indirect vicinism also plays some part, and probably affords the explanation of some reputed mutative productions of the variety.
One instance however, is very remarkable, and we have already dealt with it, when treating of constant varieties, and of the lack of vicinism in the case of species with exclusive self-fertilization. It is the "Nepaul-barley" or Hordeum trifurcatum.
Summing up the results of this long, though very incomplete, list of horticultural novelties with a more or less well-known origin, we see that sudden appearances are the rule. Having once sprung into existence the new varieties are ordinarily constant, except as affected by vicinism. Details concerning the process are mostly unavailable or at least are of very doubtful value.
Vicinism therefore, may play a part in all such cultures, enough to account for all the impurities observed in the nurseries or in commercial seed-samples. Of course this whole discussion is limited to such species as are not only as a rule visited by insects, but are dependent on these visits for their fertilization. Most of our garden-flowers are included in this category.
Students have only to recollect that specific characters prevail over varietal ones, and that every character competes only with its own antagonist. Or to give a sharper distinction: whiteness of flowers cannot be expected to be interchanged with pubescence of leaves. In concluding I will point out another danger which in the principle of vicinism may be avoided.
Keeping this rule in view, it will be easy to calculate what may be expected from spontaneous crosses for a wide range of occurrences, and thus to find an explanation of innumerable cases of apparent variability and reversion in the principle of vicinism.
They are easily multiplied by grafting, and come true from seed, at least often, and in a high proportion. Whether the original trees would yield a pure progeny if fertilized by their own pollen has as yet not been tested. The young seedlings have purple seed-leaves, and may easily be selected by this character, but they seem to be always subjected in a large measure to vicinism.
If we assume that only those seeds ripened which reverted to the early-ripening European type, and that those that remained true to the very late American variety could not reach maturity, the case seems to be wholly comprehensible, without supposing any other factors to have been at work than those of vicinism, which though unknown at the period of Metzger's and Darwin's writings, seems now to be fully understood.
Summarizing these introductory remarks we must lay stress on the fact that only a small part of the horticultural novelties are real mutations, although they do occur from time to time. If useful, they are as a rule isolated and multiplied, and if necessary, improved by selection. They are in many instances, as constant from seed as the unavoidable influence of vicinism allows them to be.
Before leaving the question of vicinism and its bearing on the general belief of the instability of varieties, which when tested with due care, prove to be quite stable, it may be as well to consider the phenomena from another point of view.
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