In horticulture this tendency is widely and vexatiously
known, since the repetition of an old variety does not bring any
advantage to the breeder. The old name of "conquests," given by the
breeders of hyacinths, tulips and other flower-bulbs to any novelty, in
disregard of the common occurrence of repetitions, is an indication of
the same experience in the repeated appearance of certain varieties.
The rule of parallel variations demands that the same character
occasionally makes its appearance in the several varieties or races,
descended from the same species, and even in widely distinct species.
This is a rule, which is very important for the general conception of
the meaning of the term variety as contrasted with elementary species.
For the recurrence of the same deviation always impresses us as a
varietal mark. Laciniated leaves are perhaps the most beautiful
instance, since they occur in so many trees and shrubs, as the walnut
tree, the beech, the birch, the hazelnut, and even in [244] brambles and
some garden-varieties of the turnip (_Brassica_).
In such cases of parallel variations the single instances obviously
follow the same rules and are therefore to be designated as analogous.
Pitchers or ascidia, formed by the union of the margins of a leaf, are
perhaps the best proof.
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