exhibit two widely different features. I will now try to make this clear
in a few words, but will return in another lecture to a fuller
discussion of this most interesting contrast.

Linnaeus himself knew that in some cases all subdivisions of a species
are of equal rank, together constituting the group called species. No
one of them outranks the others; it is not a species with varieties, but
a group, consisting only of varieties. A closer inquiry into the cases
treated in this manner by the great master of systematic science, shows
that here his varieties were exactly what we now call elementary
species.

In other cases the varieties are of a derivative nature. The species
constitutes a type that is pure in a race which ordinarily is still
growing somewhere, though in some cases it may have died out. From this
type the varieties are derived, and the way of this derivation is
usually quite manifest to the botanist. It is ordinarily [14] by the
disappearance of some superficial character that a variety is
distinguished from its species, as by the lack of color in the flowers,
of hairs on stems and foliage, of the spines and thorns, &c. Such
varieties are, strictly speaking, not to be treated in the same way as
elementary species, though they often are. We shall designate them by
the term of "retrograde varieties," which clearly indicates the nature
of their relationship to the species from which they are assumed to have
sprung. In order to lay more stress on the contrast between elementary
species and retrograde varieties, it should be stated at once, that the
first are considered to have originated from their parent-form in a
progressive way. They have succeeded in attaining something quite new
for themselves, while retrograde varieties have only thrown off some
peculiarity, previously acquired by their ancestors.