This curious behavior which is very
common, brings the plants, when young, nearer to their allies than in
the adult state, and manifestly implies that the more perfect state of
the leaves is latent throughout the life of the plant, with the
exception of the early juvenile period.
_Eucalyptus Globulus_, the Australian gum tree, has opposite and broadly
sessile leaves during the first years of its life. Later these disappear
and are replaced by long sickle-shaped foliage organs, which seem to be
scattered irregularly along the branches. The juvenile characters
manifestly lie dormant during the adult period, and that this is so, may
be shown artificially by cutting off the whole crown of the tree, when
the stem responds by producing numerous new branches, which assume the
[218] shape proper to the young trees, bearing sessile and opposite
leaves.
It seems quite unnecessary to give further instances. They are familiar
to every student. It is almost safe to say that every character has its
periods of activity and of inactivity, and numbers of flowers and fruits
can be mentioned as illustrations. One fact may be added to show that
nearly every part of the plant must have the power of producing all or
nearly all the characters of the individual to which it belongs. This
proof is given by the formation of adventitious buds.
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