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
Fritz Muller also states that a species of Bignonia and Tabernaemontana
echinata are both sterile with their own pollen in their native country
of Brazil. (9/3. Ibid 1868 page 626 and 1870 page 274.) Several
Amaryllidaceous and Liliaceous plants are in the same predicament.
Hildebrand observed with care Corydalis cava, and found it completely
self-sterile (9/4. ‘Report of the International Horticultural Congress’
1866.); but according to Caspary a few self-fertilised seeds are
occasionally produced: Corydalis halleri is only slightly self-sterile,
and C. intermedia not at all so. (9/5. ‘Botanische Zeitung’ June 27,
1873.) In another Fumariaceous genus, Hypecoum, Hildebrand observed that
H. grandiflorum was highly self-sterile, whilst H. procumbens was fairly
self-fertile. (9/6. ‘Jahrb. fur wiss. Botanik’ B. 7 page 464.)
Thunbergia alata kept by me in a warm greenhouse was self-sterile early
in the season, but at a later period produced many spontaneously
self-fertilised fruits. So it was with Papaver vagum: another species,
P. alpinum, was found by Professor H. Hoffmann to be quite self-sterile
excepting on one occasion (9/7. ‘Zur Speciesfrage’ 1875 page 47.);
whilst P. somniferum has been with me always completely self-sterile.
Eschscholtzia californica.
This species deserves a fuller consideration. A plant cultivated by
Fritz Muller in South Brazil happened to flower a month before any of
the others, and it did not produce a single capsule. This led him to
make further observations during the next six generations, and he found
that all his plants were completely sterile, unless they were crossed by
insects or were artificially fertilised with pollen from a distinct
plant, in which case they were completely fertile. (9/8. ‘Botanische
Zeitung’ 1868 page 115 and 1869 page 223.) I was much surprised at this
fact, as I had found that English plants, when covered by a net, set a
considerable number of capsules; and that these contained seeds by
weight, compared with those on plants intercrossed by the bees, as 71 to
100. Professor Hildebrand, however, found this species much more
self-sterile in Germany than it was with me in England, for the capsules
produced by self-fertilised flowers, compared with those from
intercrossed flowers, contained seeds in the ratio of only 11 to 100. At
my request Fritz Muller sent me from Brazil seeds of his self-sterile
plants, from which I raised seedlings. Two of these were covered with a
net, and one produced spontaneously only a single capsule containing no
good seeds, but yet, when artificially fertilised with its own pollen,
produced a few capsules. The other plant produced spontaneously under
the net eight capsules, one of which contained no less than thirty
seeds, and on an average about ten seeds per capsule. Eight flowers on
these two plants were artificially self-fertilised, and produced seven
capsules, containing on an average twelve seeds; eight other flowers
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