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.

Before Linnaeus, the genera were the real units of the system. De
Candolle pointed out that the old common names of plants, such as roses
and clover, poplars and oaks, nearly all refer to genera. The type of
the clovers is rich in color, and the shape of the flower-heads and the
single flowers escape ordinary observation; but notwithstanding this,
clovers are easily recognized, even if new types come to hand. White and
red clovers and many other species are distinguished simply by
adjectives, the generic name remaining the same for all.