The pistil differs in length in the two forms of every heterostyled plant, and
although a similar difference is very general with the stamens, yet in the two
forms of Linum grandiflorum and of Cordia they are equal. There can hardly be a
doubt that the relative length of these organs is an adaptation for the safe
transportal by insects of the pollen from the one form to the other. The
exceptional cases in which these organs do not stand exactly on a level in the
two forms may probably be explained by the manner in which the flowers are
visited. With most of the species, if there is any difference in the size of the
stigma of the two forms, that of the long-styled, whatever its shape may be, is
larger than that of the short-styled. But here again there are some exceptions
to the rule, for in the short-styled form of Leucosmia Burnettiana the stigmas
are longer and much narrower than those of the long-styled; the ratio between
the lengths of the stigmas in the two forms being 100 to 60. In the three
Rubiaceous genera, Faramea, Houstonia and Oldenlandia, the stigmas of the short-
styled form are likewise somewhat longer and narrower; and in the three forms of
Oxalis sensitiva the difference is strongly marked, for if the length of the two
stigmas of the long-styled pistil be taken as 100, it will be represented in the
mid- and short-styled forms by the numbers 141 and 164.
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