seedlings have sometimes by this means got included amongst the crossed
seedlings. The effect would be, as in the former case, not to exaggerate
but to diminish any average superiority of the crossed over the
self-fertilised plants.

Errors arising from the two causes just named, and from others,--such as
some of the seeds not having been thoroughly ripened, though care was
taken to avoid this error--the sickness or unperceived injury of any of
the plants,--will have been to a large extent eliminated, in those cases
in which many crossed and self-fertilised plants were measured and an
average struck. Some of these causes of error will also have been
eliminated by the seeds having been allowed to germinate on bare damp
sand, and being planted in pairs; for it is not likely that ill-matured
and well-matured, or diseased and healthy seeds, would germinate at
exactly the same time. The same result will have been gained in the
several cases in which only a few of the tallest, finest, and healthiest
plants on each side of the pots were measured.

Kolreuter and Gartner have proved that with some plants several, even as
many as from fifty to sixty, pollen-grains are necessary for the
fertilisation of all the ovules in the ovarium. (1/9. 'Kentniss der
Befruchtung' 1844 page 345. Naudin 'Nouvelles Archives du Museum' tome 1
page 27.) Naudin also found in the case of Mirabilis that if only one or
two of its very large pollen-grains were placed on the stigma, the
plants raised from such seeds were dwarfed. I was therefore careful to
give an amply sufficient supply of pollen, and generally covered the
stigma with it; but I did not take any special pains to place exactly
the same amount on the stigmas of the self-fertilised and crossed
flowers. After having acted in this manner during two seasons, I
remembered that Gartner thought, though without any direct evidence,