The second subdivision
will deal with the origin of species and varieties as taught by
experiment and observation, treating separately the sudden variations
which to my mind do produce new forms, and subsequently the fluctuations
which I hold to be not adequate to this purpose.
[32]
B. ELEMENTARY SPECIES
LECTURE II
ELEMENTARY SPECIES IN NATURE
What are species? Species are considered as the true units of nature by
the vast majority of biologists. They have gained this high rank in our
estimation principally through the influence of Linnaeus. They have
supplanted the genera which were the accepted units before Linnaeus.
They are now to be replaced in their turn, by smaller types, for reasons
which do not rest upon comparative studies but upon direct experimental
evidence.
Biological studies and practical interests alike make new demands upon
systematic botany. Species are not only the subject-material of herbaria
and collections, but they are living entities, and their life-history
and life-conditions command a gradually increasing interest. One phase
of the question is to determine the easiest manner to deal with the
collected forms of a country, and another feature is the problem [33] as
to what groups are real units and will remain constant and unchanged
through all the years of our observations.
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