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
The average height of the thirteen self-fertilised grandchildren of Hero
is 79.76 inches, and that of the grandchildren from a cross between the
self-fertilised children is 74.85; or as 100 to 94. But in Pot 4 one of
the crossed plants grew only to a height of 15 1/2 inches; and if this
plant and its opponent are struck out, as would be the fairest plan, the
average height of the crossed plants exceeds only by a fraction of an
inch that of the self-fertilised plants. It is therefore clear that a
cross between the self-fertilised children of Hero did not produce any
beneficial effect worth notice; and it is very doubtful whether this
negative result can be attributed merely to the fact of brothers and
sisters having been united, for the ordinary intercrossed plants of the
several successive generations must often have been derived from the
union of brothers and sisters (as shown in Chapter 1), and yet all of
them were greatly superior to the self-fertilised plants. We are
therefore driven to the suspicion, which we shall soon see strengthened,
that Hero transmitted to its offspring a peculiar constitution adapted
for self-fertilisation.
It would appear that the self-fertilised descendants of Hero have not
only inherited from Hero a power of growth equal to that of the ordinary
intercrossed plants, but have become more fertile when self-fertilised
than is usual with the plants of the present species. The flowers on the
self-fertilised grandchildren of Hero in Table 2.16 (the eighth
generation of self-fertilised plants) were fertilised with their own
pollen and produced plenty of capsules, ten of which (though this is too
few a number for a safe average) contained 5.2 seeds per capsule,--a
higher average than was observed in any other case with the
self-fertilised plants. The anthers produced by these self-fertilised
grandchildren were also as well developed and contained as much pollen
as those on the intercrossed plants of the corresponding generation;
whereas this was not the case with the ordinary self-fertilised plants
of the later generations. Nevertheless some few of the flowers produced
by the grandchildren of Hero were slightly monstrous, like those of the
ordinary self-fertilised plants of the later generations. In order not
to recur to the subject of fertility, I may add that twenty-one
self-fertilised capsules, spontaneously produced by the
great-grandchildren of Hero (forming the ninth generation of
self-fertilised plants), contained on an average 4.47 seeds; and this is
as high an average as the self-fertilised flowers of any generation
usually yielded.
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