My doubts have
since been strengthened by the cases of Limnanthemum and Coccocypselum, in which
the grains are of equal size in the two forms; whilst in the former genus the
pistil is nearly thrice and in the latter twice as long as in the other form. In
those species in which the grains are of unequal size in the two forms, there is
no close relationship between the degree of their inequality and that of their
pistils. Thus in Pulmonaria officinalis and in Erythroxylum the pistil in the
long-styled form is about twice the length of that in the other form, whilst in
the former species the pollen-grains are as 100 to 78, and in the latter as 100
to 93 in diameter. In the two forms of Suteria the pistil differs but little in
length, whilst the pollen-grains are as 100 to 75 in diameter. These cases seem
to prove that the difference in size between the grains in the two forms is not
determined by the length of the pistil, down which the tubes have to grow. That
with plants in general there is no close relationship between the size of the
pollen-grains and the length of the pistil is manifest: for instance, I found
that the distended grains of Datura arborea were .00243 of an inch in diameter,
and the pistil no less than 9.25 inches in length; now the pistil in the small
flowers of Polygonum fagopyrum is very short, yet the larger pollen-grains from
the short-styled plants had exactly the same diameter as those from the Datura,
with its enormously elongated pistil.
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