Whether many of the new varieties which incessantly appear are due to such occasional and accidental crosses, I do not know. Nor do I know whether the short existence of almost all the numerous varieties is the result of mere change of fashion, or of their having a weak constitution, from being the product of long-continued self- fertilisation. It may, however, be noticed that several of Andrew Knight's varieties, which have endured longer than most kinds, were raised towards the close of the last century by artificial crosses; some of them, I believe, were still vigorous in 1860; but now, in 1865, a writer, speaking (9/90. 'Gardener's Chronicle' 1865 page 387.) of Knight's four kinds of marrows, says, they have acquired a famous history, but their glory has departed.
With respect to Beans (Faba vulgaris), I will say but little. Dr. Alefield has given (9/91. 'Bonplandia' 10, 1862 s. 348.) short diagnostic characters of forty varieties. Everyone who has seen a collection must have been struck with the great difference in shape, thickness, proportional length and breadth, colour, and size which beans present. What a contrast between a Windsor and Horse-bean! As in the case of the pea, our existing varieties were preceded during the Bronze age in Switzerland (9/92. Heer 'Die Pflanzen der Pfahlbauten' 1866 s. 22.) by a peculiar and now extinct variety producing very small beans. (9/93. Mr. Bentham informs me that in Poitou and the adjoining parts of France, varieties of Phaseolus vulgaris are extremely numerous, and so different that they were described by Savi as distinct species. Mr. Bentham believes that all are descended from an unknown eastern species. Although the varieties differ so greatly in stature and in their seeds, "there is a remarkable sameness in the neglected characters of foliage and flowers, and especially in the bracteoles, an insignificant character in the eyes even of botanists.")
POTATO (Solanum tuberosum).
There is little doubt about the parentage of this plant; for the cultivated varieties differ extremely little in general appearance from the wild species, which can be recognised in its native land at the first glance. (9/94. Darwin 'Journal of Researches' 1845 page 285. Sabine in 'Transact. Hort. Soc.' volume 5 page 249.) The varieties cultivated in Britain are numerous; thus Lawson (9/95. 'Synopsis of the Vegetable Products of Scotland' quoted in Wilson's 'British Farming' page 317.) gives a description of 175 kinds. I planted eighteen kinds in adjoining rows; their stems and leaves differed but little, and in several cases there was as great a difference between the individuals of the same variety as between the different varieties. The flower varied in size, and in colour between white and purple, but in no other respect, except that in one kind the sepals were somewhat elongated. One strange variety has been described which always produces two sorts of flowers, the first double and sterile, the second single and fertile. (9/96. Sir G. Mackenzie, in 'Gardener's Chronicle' 1845 page 790.) The fruit or berries also differ, but only in a slight degree. (9/97. Putsche und Vertuch 'Versuch einer Monographie der Kartoffeln' 1819 s. 9, 15. See also Dr. Anderson 'Recreations in Agriculture' volume 4 page 325.) The varieties are liable in very different degree to the attack of the Colorado potato-beetle. (9/98. Walsh 'The American Entomologist' 1869 page 160. Also S. Tenney 'The American Naturalist' May 1871 page 171.)
The tubers, on the other hand, present a wonderful amount of diversity. This fact accords with the principle that the valuable and selected parts of all cultivated productions present the greatest amount of modification. They differ much in size and shape, being globular, oval, flattened, kidney-like, or cylindrical. One variety from Peru is described (9/99. 'Gardener's Chronicle' 1862 page 1052.) as being quite straight, and at least six inches in length, though no thicker than a man's finger. The eyes or buds differ in form, position, and colour.