But in those few plants the color was very manifest,
individually variable in degree, but always of the same blue as in the
species itself.
Many other instances could be given. Smooth varieties are seldom
absolutely so, and if scattering hairs are found on the leaves or only
on some more or less concealed parts, they correspond in their character
to those of the species. So it is with prickles, and even the thornless
thorn-apple has fruits with surfaces far from smooth. The thornless
horse-chestnut [235] has in some instances such evident protuberances on
the valves of its fruits, that it may seem doubtful whether it is a pure
and stable variety.
Systematic latency may betray itself in different ways, either by normal
systematic marks, or by atavism. With the latter I shall deal at length
on another occasion, and therefore I will give here only one very clear
and beautiful example. It is afforded by the common red clover.
Obviously the clovers, with their three leaflets in each leaf, stand in
the midst of the great family of papilionaceous plants, the leaves of
which are generally pinnate. Systematic affinity suggests that the
"three leaved" forms must have been derived from pinnate ancestors,
evidently by the reduction of the number of the leaflets. In some
species of clover the middle of the three is more or less stalked, as is
ordinarily the case in pinnate leaves; in others it is as sessile as are
its neighbors.
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