And even this latency is not a complete one, as little
scales remind us of the leaves, and traces of chlorophyll still exist in
the tissues. Numerous other cases will present themselves to every
practical botanist.
Taking for granted that characters, having once been acquired, may
become latent, and that this process is of universal occurrence
throughout the whole vegetable and animal kingdom, we may now come to a
more precise and clear conception of the existing differences between
species and varieties.
For this purpose we must take a somewhat [221] broader view of the whole
evolution of the vegetable kingdom. It is manifest that highly developed
plants have a larger number of characters than the lower groups. These
must have been acquired in some way, during preceding times. Such
evolution must evidently be called a process of improvement, or a
progressive evolution. Contrasted to this is the loss, or the latency of
characters, and this may be designated retrogressive or retrograde
evolution. But there is still a third possibility. For a latent
character may reassume its activity, return to the active state, and
become once more an important part of the whole organization. This
process may be designated as degressive evolution; it obviously
completes the series of the general types of evolution.
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