When no intercrossing with other plants of the same
stock was allowed,--that is, when the flowers were fertilised with their
own pollen in each generation--their colour in the later generations
became as uniform as that of plants growing in a state of nature,
accompanied at least in one instance by much uniformity in the height of
the plants. But in saying that the diversified tints of the flowers on
cultivated plants treated in the ordinary manner are due to differences
in the soil, climate, etc., to which they are exposed, I do not wish to
imply that such variations are caused by these agencies in any more
direct manner than that in which the most diversified illnesses, as
colds, inflammation of the lungs or pleura, rheumatism, etc., may be
said to be caused by exposure to cold. In both cases the constitution of
the being which is acted on is of preponderant importance.
CHAPTER IX.
THE EFFECTS OF CROSS-FERTILISATION AND SELF-FERTILISATION ON THE
PRODUCTION OF SEEDS.
Fertility of plants of crossed and self-fertilised parentage, both lots
being fertilised in the same manner.
Fertility of the parent-plants when first crossed and self-fertilised,
and of their crossed and self-fertilised offspring when again crossed
and self-fertilised.
Comparison of the fertility of flowers fertilised with their own pollen
and with that from other flowers on the same plant.
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