Some species of the genus _Acacia_ bear bipinnate leaves, while
others have no leaves at all, but bear broadened and flattened petioles
instead. The second type is presumed to be descended from the first by
the loss of the leaflets and the modification of the stalks into flat
and simple phyllodes. But many of them are liable to recall this
primitive form [177] when very young, in the first two or three, or
sometimes in eight or ten primary leaves. These leaves are small because
of the weakness of the young plant and therefore often more or less
reduced in structure. But they are usually strictly bipinnate and
thereby give testimony as to their descent from species which bear such
leaves throughout their life.
Other similar cases could be given, but this will suffice. They once
more show how necessary it is to separate the different cases, thrown
together until now, under this general name of atavism. It would be far
better to give them all special names, and as long as these are not
available we must be cautious not to be misguided by the name, and
especially not to confuse different phenomena with one another, because
at the present time they bear the same names.
Taking into consideration the relatively numerous restrictions resulting
from this discussion, we will now make a hasty survey of some of the
more notable and generally acknowledged cases of atavism by
bud-propagation.
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