Linnaeus himself designated the subdivisions of the species as
varieties, but in doing so he followed two clearly distinct principles.
In some cases his species were real plants, and the varieties seemed to
be derived from them by [35] some simple changes. They were subordinated
to the parent-species. In other cases his species were groups of lesser
forms of equal value, and it was not possible to discern which was the
primary and which were the derivatives.

These two methods of subdivision seem in the main, and notwithstanding
their relatively imperfect application in many single examples, to
correspond with two really distinct cases. The derivative varieties are
distinguished from the parent-species by some single, but striking mark,
and often this attribute manifests itself as the loss of some apparent
quality. The loss of spines and of hairs and the loss of blue and red
flower-colors are the most notorious, but in rarer cases many single
peculiarities may disappear, thereby constituting a variety. This
relation of varieties to the parent-species is gradually increasing in
importance in the estimation of botanists, sharply contrasting with
those cases, in which such dependency is not to be met with.

If among the subdivisions of a species, no single one can be pointed out
as playing a primary part, and the others can not be traced back to it,
the relation between these lesser units is of course of another
character. They are to be considered of equal importance. They are
distinguished from each other by more than [36] one character, often by
slight differences in nearly all their organs and qualities. Such forms
have come to be designated as "elementary species." They are only
varieties in a broad and vague systematic significance of the word, not
in the sense accorded to this term in horticultural usage, nor in a
sharper and more scientific conception.