We have lately published something on Hybridizing Plants, a subject of peculiar interest in whatever light viewed. The following interesting article is by Mr. D. Beaton, an old veteran, at present at the head of "hybridizers" in England. The article is taken from the London Journal of Horticulture and Cottage Gardener for May 14, 1861. Mr. Darwin receives but little comfort for his peculiar theory.

"Having received the following letter from Mr. Darwin, we forwarded it to Mr. Beaton, and now publish it with his reply.

"'Will Mr. Beaton, who has made such a multitude of most interesting observations on the propagation of plants, have the kindness to state whether varieties of the same species of Composite plants frequently cross each other by insect agency or other means? For instance, will any of the Cinerarias, if kept apart from other varieties, breed true? but if standing near other varieties, will they generally, or almost certainly, produce a much greater diversity of colored seedlings?

"'I saw an allusion by Mr. Beaton to this subject in THE Cottage Gardener of last year with respect to Zinnias; and from this allusion I infer that Zinnia sports much when kept separate.

"'As I am begging for information on the natural crossing of plants, I will likewise venture to inquire whether the great raisers of Hollyhocks find it necessary to keep each variety far separate from the others for raising seed. The late famous horticulturist, the Hon. and Rev. W. Herbert, when I visited him at Spofforth many years ago, remarked that he was much surprised (considering the structure of the flower and the relative periods of maturity of the pollen and stigma) how true some sorts of Hollyhocks bred, even when growing close to other varieties. I have found this to be the case with some of the varieties, and can not understand how it is possible. Mr. Beaton might, if he pleased, write an article, very valuable to physiological botanists and of some practical utility, on the natural crossing of varieties. He might indicate in which genera crossing most commonly occurred, and in which it seldom or never occurred. For instance, I have observed Sweet Peas during several years, and believe that they never cross; and it is not easy to make an artificial cross, though I succeeded at last, but got no good in a horticultural point of view. - Charles Darwin, Down, Bromley, Kent.'

"I am not aware that any two species of Composite plants under cultivation have ever been crossed by man, or through the agency of insects. Mr. Penny, who first broke down Cineraria cruenta in the Messrs. Young's nursery at Epsom, said he got it to cross with another species, I think, from Teneriffe. It is more in accordance with the experience of cross-breeders, however, that superior cultivation induced the disposition to vary, as in the Dahlia. The Swan River Daisy, Brachycome iberidifolia, is the last instance we have of this in the garden; while Zinnia is the last variable Composite plant that has been turned into double flowers, so called. This last change is said to have been effected in India; and if it is really so, the effect may be ascribed to climate more than to high cultivation. We know the Port Natal Gladiolus (natalensis or psittacinus) could not be crossed here, or on the Continent, with any of the old Cape species or their seedlings; but in Australia, at Sydney, the cross was easily effected, Gandavensis being the first seedling of that cross; but as soon as that cross got into the hands of European cultivators they experienced no more difficulty in pushing on their crosses in the strain of natalensis.

These are three recent instances of the undoubted influence of cultivation and climate over genuine wild species. For the first seven or eight years of high cultivation the Swan River Daisy kept to its original colors - blue and white - then varied into lilac and purple and minor shades. When a flower or species thus varies from the effects of cultivation or climate, the variation is also variable in degree. Some of the varieties reproduce themselves quite true from seed from the first; others, on the contrary, take some years before the color or habit is 'fixed,' as gardeners say when a variable plant comes true from seeds after sporting for some years; and some never get fixed, or have not done so yet, and Zinnia is an instance of it. In all these instances some people attribute the changes to cross-fertilization; they have been crossing their flowers, and they have seen results, and account for them that way, deceiving themselves. But those who have studied and experimented on the effect of cross-breeding, as against the results of the effects of climate and cultivation, have long since arrived at the conclusion that crossing has no power on fixing any two plants which naturally sport; that is to say, on fixing a seedling from their union combining so much of the qualities of each of the parents as is generally the case when two permanent kinds or species, which always reproduce themselves or their like, are united.

That conclusion strikes at the root of the fallacy which obtains in respect to the best means of improving all our domestic fruits; and yet crossing is an element of great value in improving flowers and fruit, which seems a contradiction, but is explained thus: Some seedlings from plants that have been crossed for a generation come quite true from seeds, some half true, and some on which no reliance whatever can be placed, or, in our language, they always sport from seed. On those which this sport-crossing has no effect - such, however, as come half true and half sport-crossing - there is a chance of an intermediate condition, and those merest varieties which come true from seeds crossing is just as effectual with them as with two genuine wild species. One would think therefore, there were no natural limits or difference between a species and a permanent variety; that is, one which comes true from seed, like the large-flowering variety of the Mignonette. In practice there is no landmark whatever between such a variety and a wild species.