This led me carefully
to observe during four years many seedlings, raised from several
illegitimate unions. The chief result is that these illegitimate plants,
as they may be called, are not fully fertile. It is possible to raise from
dimorphic species, both long-styled and short-styled illegitimate plants,
and from trimorphic plants all three illegitimate forms. These can then be
properly united in a legitimate manner. When this is done, there is no
apparent reason why they should not yield as many seeds as did their
parents when legitimately fertilised. But such is not the case. They are
all infertile, in various degrees; some being so utterly and incurably
sterile that they did not yield during four seasons a single seed or even
seed-capsule. The sterility of these illegitimate plants, when united with
each other in a legitimate manner, may be strictly compared with that of
hybrids when crossed inter se. If, on the other hand, a hybrid is crossed
with either pure parent-species, the sterility is usually much lessened:
and so it is when an illegitimate plant is fertilised by a legitimate
plant. In the same manner as the sterility of hybrids does not always run
parallel with the difficulty of making the first cross between the two
parent-species, so that sterility of certain illegitimate plants was
unusually great, while the sterility of the union from which they were
derived was by no means great.
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