-
7 100: 81 -
8 100: 85 -
9 100: 79 100: 26 (Number of capsules)
10 100: 54 -

Taking the average, the ratio as regards growth is 100:77. The
considerable superiority of the crossed plants is apparent in the first
generation and is not increased in the following generations; but there
is some fluctuation about the average ratio. The numbers representing
the fertility of crossed and self-fertilised plants are more difficult
to compare with accuracy; the superiority of the crossed plants is
chiefly explained by the fact that they produce a much larger number
of capsules, not because there are on the average more seeds in each
capsule. The ratio of the capsules was, e.g. in the third generation,
100:38, that of the seeds in the capsules 100:94. It is also especially
noteworthy that in the self-fertilised plants the anthers were smaller
and contained a smaller amount of pollen, and in the eighth generation
the reduced fertility showed itself in a form which is often found in
hybrids, that is the first flowers were sterile. (Complete sterility was
not found in any of the plants investigated by Darwin. Others appear
to be more sensitive; Cluer found Zea Mais "almost sterile" after three
generations of self-fertilisation. (Cf. Fruwirth, "Die Zuchtung der
Landwirtschaftlichen Kulturpflanzen", Berlin, 1904, II. page 6.))

The superiority of crossed individuals is not exhibited in the same
way in all plants. For example in Eschscholzia californica the crossed
seedlings do not exceed the self-fertilised in height and vigour,
but the crossing considerably increases the plant's capacity for
flower-production, and the seedlings from such a mother-plant are more
fertile.

The conception implied by the term crossing requires a closer analysis.
As in the majority of plants, a large number of flowers are in bloom
at the same time on one and the same plant, it follows that insects
visiting the flowers often carry pollen from one flower to another of
the same stock. Has this method, which is spoken of as Geitonogamy, the
same influence as crossing with pollen from another plant? The results
of Darwin's experiments with different plants (Ipomoea purpurea,
Digitalis purpurea, Mimulus luteus, Pelargonium, Origanum) were not in
complete agreement; but on the whole they pointed to the conclusion that
Geitonogamy shows no superiority over self-fertilisation (Autoga