But this and some other sources of
error will presently be discussed. In some few cases of spontaneously
self-fertile species, the flowers were allowed to fertilise themselves
under the net; and in still fewer cases uncovered plants were allowed to
be freely crossed by the insects which incessantly visited them. There
are some great advantages and some disadvantages in my having
occasionally varied my method of proceeding; but when there was any
difference in the treatment, it is always so stated under the head of
each species.
Care was taken that the seeds were thoroughly ripened before being
gathered. Afterwards the crossed and self-fertilised seeds were in most
cases placed on damp sand on opposite sides of a glass tumbler covered
by a glass plate, with a partition between the two lots; and the glass
was placed on the chimney-piece in a warm room. I could thus observe the
germination of the seeds. Sometimes a few would germinate on one side
before any on the other, and these were thrown away. But as often as a
pair germinated at the same time, they were planted on opposite sides of
a pot, with a superficial partition between the two; and I thus
proceeded until from half-a-dozen to a score or more seedlings of
exactly the same age were planted on the opposite sides of several pots.
If one of the young seedlings became sickly or was in any way injured,
it was pulled up and thrown away, as well as its antagonist on the
opposite side of the same pot.
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