6.
Short-styled form, mid-length stamens (20 measurements): 12.3.
We have here the usual rule of the grains from the longer stamens, the tubes of
which have to penetrate the longer pistil, being larger than those from the
stamens of less length. The extreme difference in diameter between the grains
from the longest stamens of the mid-styled form, and from the shortest stamens
of the long-styled, is as 16.4 to 9.0, or as 100 to 55; and this is the greatest
difference observed by me in any heterostyled plant. It is a singular fact that
the grains from the corresponding longest stamens in the two forms differ
considerably in diameter; as do those in a lesser degree from the corresponding
mid-length stamens in the two forms; whilst those from the corresponding
shortest stamens in the long- and mid-styled forms are almost exactly equal.
Their inequality in the two first cases depends on the grains in both sets of
anthers in the short-styled form being smaller than those from the corresponding
anthers in the other two forms; and here we have a case parallel with that of
the mid-styled form of Lythrum salicaria. In this latter plant the pollen-grains
of the mid-styled forms are of smaller size and have less fertilising power than
the corresponding ones in the other two forms; whilst the ovarium, however
fertilised, yields a greater number of seeds; so that the mid-styled form is
altogether more feminine in nature than the other two forms.
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