As a rule they appear in
large sowings, only one, or only a few at a time. Many of them have not
been observed during their youth, but only after having been planted out
in parks and forests, since the weeping characters show only after
several years.
The monophyllous bastard-acacia originated in the same way. Its
peculiarities will be dealt with on another occasion, but the
circumstances of its birth may as well be given here. In 1855 in the
nursery of Deniau, at Brain-sur-l'Authion (Maine et Loire), it appeared
in a lot of [618] seedlings of the typical species in a single
individual. This was transplanted into the Jardin des Plantes at Paris,
where it flowered and bore seeds in 1865. It must have been partly
pollinated by the surrounding normal representatives of the species,
since the seeds yielded only one-fourth of true offspring. This
proportion, however, has varied in succeeding years. Briot remarks that
the monophyllous bastard acacia is liable to petaloid alterations of its
stamens, which deficiency may encroach upon its fertility and
accordingly upon the purity of its offspring.
Broom-like varieties often occur among trees, and some are known for
their very striking reversions by buds, as we have seen on a previous
occasion. They are ordinarily called pyramidal or fastigiate forms, and
as far as their history goes, they arise suddenly in large sowings of
the normal species.
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