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Darwin, Charles, 1809-1882

"Effects of Cross and Self Fertilisation in the Vegetable Kingdom"


The winter of 1870-1871 was severe. In the spring the three crossed
plants in Pot 2 had not even the tips of their shoots in the least
injured, whereas all three self-fertilised plants were killed half-way
down to the ground; and this shows how much more tender they were. In
consequence not one of these latter plants bore a single flower during
the ensuing summer of 1871, whilst all three crossed plants flowered.
Ononis minutissima.
This plant, of which seeds were sent me from North Italy, produces,
besides the ordinary papilionaceous flowers, minute, imperfect, closed
or cleistogene flowers, which can never be cross-fertilised, but are
highly self-fertile. Some of the perfect flowers were crossed with
pollen from a distinct plant, and six capsules thus produced yielded on
an average 3.66 seeds, with a maximum of five in one. Twelve perfect
flowers were marked and allowed to fertilise themselves spontaneously
under a net, and they yielded eight capsules, containing on an average
2.38 seeds, with a maximum of three seeds in one. So that the crossed
and self-fertilised capsules from the perfect flowers yielded seeds in
the proportion of 100 to 65. Fifty-three capsules produced by the
cleistogene flowers contained on an average 4.1 seeds, so that these
were the most productive of all; and the seeds themselves looked finer
even than those from the crossed perfect flowers.


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