This section is from the book "The Gardener's Monthly And Horticulturist V22", by Thomas Meehan. See also: Four-Season Harvest: Organic Vegetables from Your Home Garden All Year Long.
The Garden says: " I fancy insect agency is talked of in a very unscientific way by too enthusiastic followers of Mr. Darwin. I remember reading Professor Riley's dogma that the Yucca could only possibly be fertilized by a certain American insect, and being amused at it because I had several times seen it fruiting well in the south of Europe, and also in France. Probably we should see it oftener if we had a better climate. I now note that Mr. Ellacombe, writing to a contemporary, says: There can be no doubt that the Yucca can be fertilized by other means than by the agency of the Yucca moth (Pronuba yuccasella). I have more than once had well-formed fruit on Y. recurvifolia, but the seeds did not come to maturity. Dr. Engelmann in his " Notes on the Genus Yucca," says: ' In the botanical garden of Venice I gathered the pulpy pods from a large Yucca aloifolia, about fifteen feet high.' This was the only Yucca fruit seen by me in Europe, though I have since learned that in other instances also, though only exceptionally, fruit and good seed have been produced there, principally by the same species, and very rarely by others.
I remember the late Mr. Barillet telling me he had raised a great many varieties of Yucca gloriosa from seed saved in France. However, this mistake on the part of so good a man as Riley, is good sense compared with what we read on this side as to the influence of insects on the color and odors of plants. The statement by Mr. Wallace, for example, that showy flowers are scentless because from their color they are sufficiently attractive to insects may pass for science with some innocent people, but it seems foolish to those who know even only a few garden plants".
There is no doubt in our mind but that too much is made of the color, odor, and other properties of flowers in relation to insect habits, and perhaps Prof. Riley may in his enthusiasm, have made the mistake which all useful enthusiasts are liable to make, of not being quite logical when putting " this and that together," on a review of his facts. But there is nothing more certain than that Prof. Riley is right in regarding the Yucca, seldom if ever fertilized except by outside aid: and if the Yucca seeds in Europe, it would be well to see whether there is not some nocturnal insect engaged in the work, if indeed the Pronuba itself, may not have been imported there. It must be remembered that the insect, though amidst active entomologists for a hundred years in immense abundance, was not known till Prof. Riley found it a few years ago.