Delpino believes
that cleistogamic flowers have been developed in order to ensure the production
of seeds under climatic or other conditions which tend to prevent the
fertilisation of the perfect flowers. (8/29. 'Sull' Opera la Distribuzione dei
Sessi nelle Piante' 1867 page 30.) I do not doubt that this holds good to a
certain limited extent, but the production of a large supply of seeds with
little consumption of nutrient matter or expenditure of vital force is probably
a far more efficient motive power. The whole flower is much reduced in size; but
what is much more important, an extremely small quantity of pollen has to be
formed, as none is lost through the action of insects or the weather; and pollen
contains much nitrogen and phosphorus. Von Mohl estimated that a single
cleistogamic anther-cell of Oxalis acetosella contained from one to two dozen
pollen-grains; we will say 20, and if so the whole flower can have produced at
most 400 grains; with Impatiens the whole number may be estimated in the same
manner at 250; with Leersia at 210; and with Viola nana at only 100. These
figures are wonderfully low compared with the 243,600 pollen-grains produced by
a flower of Leontodon, the 4,863 by an Hibiscus, or the 3,654,000 by a Paeony.
(8/30. The authorities for these statements are given in my 'Effects of Cross
and Self-Fertilisation' page 376.
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