Species and Varieties, Their Origin by Mutation | Page 7

Pedigree-culture is the method required and any form which remains

constant and distinct from its allies in the garden is to be considered as
an elementary species.
In the following lectures we shall consider this point at length, to show
the compound nature of systematic species in wild and in cultivated
plants. In both cases, the principle is becoming of great importance, and
many papers published recently indicate its almost universal
acceptation.
Among the systematic subdivisions of species, not all have the same
claim to the title of elementary species. In the first place the cases in
which the differences may occur between parts of the same individual
are to be excluded. Dividing an alpine plant into two halves and [13]
planting one in a garden, varietal differences at once arise and are often
designated in systematic works under different varietal names.
Secondly all individual differences which are of a fluctuating nature are
to be combined into a group. But with these we shall deal later.
Apart from these minor points the subdivisions of the systematic
species 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.
The whole vegetable kingdom exhibits a constant struggle between
progression and retrogression. Of course, the great lines of the general
pedigree are due to progression, many single steps in this direction
leading together to the great superiority of the flowering plants over
their cryptogamous ancestors. But progression is nearly always
accompanied by retrogression in the principal lines of evolution, [15]
as well as in the collateral branches of the genealogical tree. Sometimes
it prevails, and the monocotyledons are obviously a reduced branch of
the primitive dicotyledons. In orchids and aroids, in grasses and sedges,
reduction plays a most important part, leaving its traces on the flowers
as well as on the embryo of the seed. Many instances could be given to
prove that progression and retrogression are the two main principles of
evolution at large. Hence the conclusion, that our analysis must dissect
the complicated phenomena of evolution so far as to show the separate
functions of these two contrasting principles. Hundreds of steps were
needed to evolve the family of the orchids, but the experimenter must
take the single steps for the object of his inquiry. He finds that some are
progressive and others retrogressive and so his investigation falls under
two heads, the origin of progressive characters, and the subsequent loss
of the same. Progressive steps are the marks of elementary species,
while retrograde varieties are distinguished by apparent losses. They
have equal claim to our interest and our study.
As already stated I propose to deal first with the elementary species and
afterwards with the retrograde varieties. I shall try to depict them to you
in the first place as they are seen in [16] nature and in culture, leaving
the question of their origin to a subsequent experimental treatment.
The question of the experimental origin of new species and varieties
has to be taken up from two widely separated starting points.