The Effects of Cross & Self-Fertilisation in the Vegetable KingdomDarwin, Charles
Science
The Effects of Cross & Self-Fertilisation in the Vegetable Kingdom
Darwin, Charles
Fertilization of plants; Plants -- Variation; Pollination
advantage; so that the self-fertilised plants, taken altogether, were
somewhat superior to the quasi-crossed plants. In this case, as in that
of the Origanum, if individuals which have been asexually propagated
from the same stock, and which have been long subjected to the same
conditions, are crossed, no advantage whatever is gained.
Several flowers on another plant of the same variety were fertilised
with pollen from the younger flowers on the same plant, so as to avoid
using the old and long-shed pollen from the same flower, as I thought
that this latter might be less efficient than fresh pollen. Other
flowers on the same plant were crossed with fresh pollen from a plant
which, although closely similar, was known to have arisen as a distinct
seedling. The self-fertilised seeds germinated rather before the others;
but as soon as I got equal pairs they were planted on the opposite sides
of four pots.
TABLE 5/49. Pelargonium zonale.
Heights of plants measured in inches.
Column 1: Number (Name) of Pot.
Column 2: Crossed Plants.
Column 3: Self-fertilised Plants.
Pot 1 : 22 3/8 : 25 5/8.
Pot 1 : 19 6/8 : 12 4/8.
Pot 2 : 15 : 19 6/8.
Pot 2 : 12 2/8 : 22 3/8.
Pot 3 : 30 5/8 : 19 4/8.
Pot 3 : 18 4/8 : 7 4/8.
Pot 4 : 38 : 9 1/8.
Total : 156.50 : 116.38.
When the two lots of seedlings were between 4 and 5 inches in height
they were equal, excepting in Pot 4, in which the crossed plant was much
the tallest. When between 11 and 14 inches in height, they were measured
to the tips of their uppermost leaves; the crossed averaged 13.46, and
the self-fertilised 11.07 inches in height, or as 100 to 82. Five months
later they were again measured in the same manner, and the results are
given in Table 5/49.
The seven crossed plants now averaged 22.35, and the seven
self-fertilised 16.62 inches in height, or as 100 to 74. But from the
great inequality of the several plants, the result is less trustworthy
than in most other cases. In Pot 2 the two self-fertilised plants always
had an advantage, except whilst quite young over the two crossed plants.
As I wished to ascertain how these plants would behave during a second
growth, they were cut down close to the ground whilst growing freely.
The crossed plants now showed their superiority in another way, for only
one out of the seven was killed by the operation, whilst three of the
self-fertilised plants never recovered. There was, therefore, no use in
keeping any of the plants excepting those in Pots 1 and 3; and in the
following year the crossed plants in these two pots showed during their
second growth nearly the same relative superiority over the
self-fertilised plants as before.
Tropaeolum minus.
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