But in
vain. Contradiction and doubt still reign supreme. All our hopes now
rest on the result of experiments.
Unfortunately such experiments seemed simply impossible a few years ago.
What is to guide us in the choice of the material? The answer may only
be expected from a consideration of elementary species. For it is
obvious that they only can be observed to originate, and that the
systematic species, because they are only artificial groups of lower
unities, can never become the subject of successful experimental
inquiry.
In previous lectures we tried to clear up the differences existing
between nearly related elementary species. We have seen that they affect
all of the attributes of the plants, each of them changing in some
measure all of the organs. Nevertheless they were due to distinct
unities and of the lowest possible degree. Such unit-steps may therefore
be expected to become visible some time or other by artificial means. On
the other hand, mutations as a rule make their appearance in groups, and
there are many systematic species which on close inspection [518] have
been shown to be in reality composite assemblages. Roses and brambles,
hawkweeds and willows are the best known examples. Violets and _Draba
verna_, dandelions and helianthemums and many other instances were dealt
with in previous lectures.
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