Moreover,
the longer stamens of the long-styled form of Pontederia, and the shorter ones
of the short-styled form are placed in a proper position for fertilising the
stigma of a mid-styled form. But Fritz Muller, although he examined a vast
number of plants, could never find one belonging to the mid-styled form. The
older flowers of the long-styled and short-styled plants had set plenty of
apparently good fruit; and this might have been expected, as they could
legitimately fertilise one another. Although he could not find the mid-styled
form of this species, he possessed plants of another species growing in his
garden, and all these were mid-styled; and in this case the pollen-grains from
the anthers of the longer stamens were to those from the shorter stamens of the
same flower as 100 to 86 in diameter, as deduced from ten measurements of each
kind. These mid-styled plants growing by themselves never produced a single
fruit.
Considering these several facts, there can hardly be a doubt that both these
species of Pontederia are heterostyled and trimorphic. This case is an
interesting one, for no other Monocotyledonous plant is known to be
heterostyled. Moreover, the flowers are irregular, and all other heterostyled
plants have almost symmetrical flowers. The two forms differ somewhat in the
colour of their corollas, that of the short-styled being of a darker blue,
whilst that of the long-styled tends towards violet, and no other such case is
known.
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