This discussion seems to throw some light on the increase of leaflets in
the clover. The pea family, or the group of papilionaceous plants, has
pinnate leaves ordinarily, which, according to our premises, must be
considered as a derivative type. In the clovers and their allies this
type reverts halfway to the single form, producing only three leaflets
on each stalk. If now the clover increases its number of leaflets, this
may be considered as a reversion to its nearest progenitors, the
papilionaceous plants with pinnate leaves. Hence a halfway returning and
therefore positive atavism. And as I have already mentioned in a former
lecture, pinnate [345] leaves are also sometimes produced by my new race
of clover.
Returning to the original plants of this race, it is evidently
impossible to decide whether they were really the beginning of a new
strain, and had originated themselves by some sudden change from the
common type, or whether they belonged to an old variety, which had
propagated itself perhaps during centuries, unobserved by man. But the
same difficulty generally arises when new varieties are discovered. Even
the behavior of the plants themselves or of their progeny does not
afford any means of deciding the question. The simplest way of stating
the matter therefore, is to say that I accidentally found two
individuals of the "five-leaved" race.
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