The Different Forms of Flowers on Plants of the Same SpeciesDarwin, Charles
Science
The Different Forms of Flowers on Plants of the Same Species
Darwin, Charles
Fertilization of plants; Heterostylism; Plant physiology; Plants -- Variation; Pollination
It is impossible to look at the above table and doubt that the legitimate unions
between the two forms of the above nine species of Primula are much more fertile
than the illegitimate unions; although in the latter case pollen was always
taken from a distinct plant of the same form. There is, however, no close
correspondence in the two rows of figures, which give, according to the two
standards, the difference of fertility between the legitimate and illegitimate
unions. Thus all the flowers of P. Sinensis which were illegitimately fertilised
by Hildebrand produced capsules; but these contained only 42 per cent of the
number of seeds yielded by the legitimately fertilised capsules. So again, 95
per cent of the illegitimately fertilised flowers of P. Sikkimensis produced
capsules; but these contained only 31 per cent of the number of seeds in the
legitimate capsules. On the other hand, with P. elatior only 27 per cent of the
illegitimately fertilised flowers yielded capsules; but these contained nearly
75 per cent of the legitimate number of seeds. It appears that the setting of
the flowers, that is, the production of capsules whether good or bad, is not so
much influenced by legitimate and illegitimate fertilisation as is the number of
seeds which the capsules contain. For, as may be seen at the bottom of Table
1.12, 88.4 per cent of the illegitimately fertilised flowers yielded capsules;
but these contained only 61.8 per cent of seeds, in comparison, in each case,
with the legitimately fertilised flowers and capsules of the same species.
There is another point which deserves notice, namely, the relative degree of
infertility in the several species of the long-styled and short-styled flowers,
when both are illegitimately fertilised. The data may be found in the earlier
tables, and in those given by Mr. Scott in the Paper already referred to. If we
call the number of seeds per capsule produced by the illegitimately fertilised
long-styled flowers 100, the seeds from the illegitimately fertilised short-
styled flowers will be represented by the following numbers (Table 1.a.):--
TABLE 1.a.
Primula veris : 71.
Primula elatior : 44 (Probably too low).
Primula vulgaris : 36 (Perhaps too low).
Primula Sinensis : 71.
Primula auricula : 119.
Primula Sikkimensis : 57.
Primula cortusoides : 93.
Primula involucrata : 74.
Primula farinosa : 63.
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