The colour of the green pollen in the longest stamens is variable,
being sometimes pale greenish-yellow; in one short-styled plant it was almost
white. The grains vary a little in size: I examined one short-styled plant with
the grains from the mid-length and shortest anthers of the same size. We here
see great variability in many important characters; and if any of these
variations were of service to the plant, or were correlated with useful
functional differences, the species is in that state in which natural selection
might readily do much for its modification.
ON THE POWER OF MUTUAL FERTILISATION BETWEEN THE THREE FORMS.
Nothing shows more clearly the extraordinary complexity of the reproductive
system of this plant, than the necessity of making eighteen distinct unions in
order to ascertain the relative fertilising power of the three forms. Thus the
long-styled form has to be fertilised with pollen from its own two kinds of
anthers, from the two in the mid-styled, and from the two in the short-styled
form. The same process has to be repeated with the mid-styled and short-styled
forms. It might have been thought sufficient to have tried on each stigma the
green pollen, for instance, from either the mid- or short-styled longest
stamens, and not from both; but the result proves that this would have been
insufficient, and that it was necessary to try all six kinds of pollen on each
stigma.
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