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
This species, which bears pink flowers, was introduced from the Cape of Good
Hope. A sketch of the reproductive organs of the three forms (Figure 4.11) has
already been given. The stigma of the long-styled form (with the papillae on its
surface included) is twice as large as that of the short-styled, and that of the
mid-styled intermediate in size. The pollen-grains from the stamens in the three
forms are in their longer diameters as follows:--
Table 4.c. Oxalis speciosa. Diameters of pollen-grains in divisions of the
micrometer.
Column 1: Source of Pollen-grains.
Column 2: Minimum diameter.
Column 3: Maximum diameter.
From the:
Longest stamens of short-styled form : 15 to 16.
Mid-length stamens of short-styled form : 12 to 13.
Longest stamens of mid-styled form : 16.
Shortest stamens of mid-styled form : 11 to 12.
Mid-length stamens of long-styled form : 14.
Shortest stamens of long-styled form : 12.
Therefore the extreme difference in diameter is as 16 to 11, or as 100 to 69;
but as the measurements were taken at different times, they are probably only
approximately accurate. The results of my experiments in fertilising the three
forms are given in Table 4.29.
Table 4.29. Oxalis speciosa.
Column 1: Nature of the Union.
Column 2: Number of Flowers fertilised.
Column 3: Number of Capsules produced.
Column 4: Average Number of Seeds per Capsule.
Long-styled by pollen of longest stamens of short-styled. Legitimate union :
19 : 15 : 57.4.
Long-styled by pollen of longest stamens of mid-styled. Legitimate union :
4 : 3 : 59.0.
Long-styled by pollen of own-form mid-length stamens. Illegitimate union :
9 : 2 : 42.5.
Long-styled by pollen of own-form shortest stamens. Illegitimate union :
11 : 0 : 0.
Long-styled by pollen of shortest stamens of mid-styled. Illegitimate union :
4 : 0 : 0.
Long-styled by pollen of mid-length stamens of short-styled. Illegitimate union
:
12 : 5 : 30.0.
Mid-styled by pollen of mid-length stamens of long-styled. Legitimate union :
3 : 3 : 63.6.
Mid-styled by pollen of mid-length stamens of short-styled. Legitimate union :
4 : 4 : 56.3.
Mid-styled by mixed pollen from both own-form longest and shortest stamens.
Illegitimate union :
9 : 2 : 19.
Mid-styled by pollen of longest stamens of short-styled. Illegitimate union :
12 : 1 : 8.
Short-styled by pollen of shortest stamens of mid-styled. Legitimate union:
3 : 2 : 67.
Short-styled by pollen of shortest stamens of long-styled. Legitimate union:
3 : 3 : 54.3.
Short-styled by pollen of own-form longest stamens. Illegitimate union:
5 : 1 : 8.
Short-styled by pollen of own-form mid-length stamens. Illegitimate union :
3 : 0 : 0.
Short-styled by both pollens mixed together, of own-form longest and mid-length
stamens. Illegitimate union:
13 : 0 : 0.
Short-styled by pollen of longest stamens of mid-styled. Illegitimate union :
7 : 0 : 0.
Short-styled by pollen of mid-length stamens of long-styled. Illegitimate union:
10 : 1 : 54.
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