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
Having ascertained, by leaving crossed and self-fertilised seed on damp
sand, that they germinated simultaneously, both kinds were thickly sown
on opposite sides of a broad and rather shallow pan; so that the two
sets of seedlings, which came up at the same time, were subjected to the
same unfavourable conditions. This was a bad method of treatment, but
this species was one of the first on which I experimented. When the
crossed seedlings were on an average half an inch high, the
self-fertilised ones were only a quarter of an inch high. When grown to
their full height under the above unfavourable conditions, the four
tallest crossed plants averaged 7.62, and the four tallest
self-fertilised 5.87 inches in height; or as 100 to 77. Ten flowers on
the crossed plants were fully expanded before one on the self-fertilised
plants. A few of these plants of both lots were transplanted into a
large pot with plenty of good earth, and the self-fertilised plants, not
now being subjected to severe competition, grew during the following
year as tall as the crossed plants; but from a case which follows it is
doubtful whether they would have long continued equal. Some flowers on
the crossed plants were crossed with pollen from another plant, and the
capsules thus produced contained a rather greater weight of seed than
those on the self-fertilised plants again self-fertilised.
CROSSED AND SELF-FERTILISED PLANTS OF THE SECOND GENERATION.
Seeds from the foregoing plants, fertilised in the manner just stated,
were sown on the opposite sides of a small pot (1) and came up crowded.
The four tallest crossed seedlings, at the time of flowering, averaged 8
inches in height, whilst the four tallest self-fertilised plants
averaged only 4 inches. Crossed seeds were sown by themselves in a
second small pot, and self-fertilised seeds were sown by themselves in a
third small pot so that there was no competition whatever between these
two lots. Nevertheless the crossed plants grew from 1 to 2 inches higher
on an average than the self-fertilised. Both lots looked equally
vigorous, but the crossed plants flowered earlier and more profusely
than the self-fertilised. In Pot 1, in which the two lots competed with
each other, the crossed plants flowered first and produced a large
number of capsules, whilst the self-fertilised produced only nineteen.
The contents of twelve capsules from the crossed flowers on the crossed
plants, and of twelve capsules from self-fertilised flowers on the
self-fertilised plants, were placed in separate watch-glasses for
comparison; and the crossed seeds seemed more numerous by half than the
self-fertilised.
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