ty {330} years, which always came true.
From the analogy of kidney-beans I should have expected[604] that
occasionally, perhaps at long intervals of time, when some slight
degree of sterility had supervened from long-continued
self-fertilisation, varieties thus growing near each other would have
crossed; and I shall give in the eleventh chapter two cases of distinct
varieties which spontaneously intercrossed, as shown (in a manner
hereafter to be explained) by the pollen of the one variety having
acted directly on the seeds of the other. Whether the incessant supply
of new varieties is partly due to such occasional and accidental
crosses, and their fleeting existence to changes of fashion; or again,
whether the varieties which arise after a long course of continued
self-fertilisation are weakly and soon perish, I cannot even
conjecture. 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, in 1860, vigorous; but now, in 1865, a
writer, speaking[605] 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.
Alefeld has given[606] short diagnostic characters of forty varieties.
Every one 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 by a peculiar and now
extinct variety producing very small beans.[607]

_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.[608] The varieties
cultivated in Britain are numerous; thus Lawson[609] 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 an amount of difference between the individuals of the
sam