I know this from my own experiments on Ipomoea, given in the
Introduction; and it is still more plainly shown by the astonishingly
small quantity produced by cleistogene flowers, which lose none of their
pollen, in comparison with that produced by the open flowers borne by
the same plants; and yet this small quantity suffices for the
fertilisation of all their numerous seeds. Mr. Hassall took pains in
estimating the number of pollen-grains produced by a flower of the
Dandelion (Leontodon), and found the number to be 243,600, and in a
Paeony 3,654,000 grains. (10/9. 'Annals and Magazine of Natural History'
volume 8 1842 page 108.) The editor of the 'Botanical Register' counted
the ovules in the flowers of Wistaria sinensis, and carefully estimated
the number of pollen-grains, and he found that for each ovule there were
7000 grains. (10/10. Quoted in 'Gardeners' Chronicle' 1846 page 771.)
With Mirabilis, three or four of the very large pollen-grains are
sufficient to fertilise an ovule; but I do not know how many grains a
flower produces. With Hibiscus, Kolreuter found that sixty grains were
necessary to fertilise all the ovules of a flower, and he calculated
that 4863 grains were produced by a single flower, or eighty-one times
too many. With Geum urbanum, however, according to Gartner, the pollen
is only ten times too much. (10/11. Kolreuter 'Vorlaufige Nachricht'
1761 page 9.
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