cut or
mutilated.[423] So it is with hybrids; for instance, Prof. Lecoq[424]
had three plants of Mirabilis, which, though they grew luxuriantly and
flowered, were quite sterile; but after beating one with a stick until
a few branches alone were left, these at once yielded good seed. The
sugar-cane, which grows vigorously and produces a large supply of
succulent stems, never, according to various observers, bears seed in
the West Indies, Malaga, India, Cochin China, or the Malay
Archipelago.[425] Plants which produce a large number of tubers are apt
to be sterile, as occurs, to a certain extent, with the common potato;
and Mr. Fortune informs me that the sweet potato (_Convolvulus
batatas_) in China never, as far as he has seen, yields seed. Dr. Royle
remarks[426] that in India the _Agave vivipara_, when grown in rich
soil, invariably produces bulbs, but no seeds; whilst a poor soil and
dry climate leads to an opposite result. In China, according to Mr.
Fortune, an extraordinary number of little bulbs are developed in the
axils of the leaves of the yam, and this plant does not bear seed.
Whether in these cases, as in those of double flowers and seedless
fruit, sexual sterility from changed conditions of life is the primary
cause which leads to the excessive development of the organs of
vegetation, is doubtful; though some evidence might be advanced in
favour of this view. It is perhaps a more probable view that plants
which propagate themselves largely by one method, namely by buds, have
not sufficient vital power or organised matter for the other method of
sexual generation.

Several distinguished botanists and good practical judges believe that
long-continued propagation by cuttings, runners, tubers, bulbs, &c.,
independently of any excessive development of these parts, is the cause
of many plants failing to produce flowers and of others failing to
produce fertile flowers,--it is as if they had lost the habit of sexual
generation.[427] That many plants when thus propagated are sterile
there can be no doubt, but whether the long continuance of this form of
propagation is the actual cause of their sterility, I will not venture,
from the want of sufficient evidence, to express an opinion.

That plants may be propagated for long periods by buds, without the aid
of sexual generation, w