transmissible variations, by ordering and arranging these, selecting them
in relation to their number and size, as the architect does his building-
stones so that a particular style must result. ("Variation under
Domestication", 1875 II. pages 426, 427.) But the building-stones
themselves, the variations, have their basis in the influences which cause
variation in those vital units which are handed on from one generation to
another, whether, taken together they form the WHOLE organism, as in
Bacteria and other low forms of life, or only a germ-substance, as in
unicellular and multicellular organisms. (The Author and Editor are
indebted to Professor Poulton for kindly assisting in the revision of the
proof of this Essay.)


IV. VARIATION.

By HUGO DE VRIES,
Professor of Botany in the University of Amsterdam.

I. DIFFERENT KINDS OF VARIABILITY.

Before Darwin, little was known concerning the phenomena of variability.
The fact, that hardly two leaves on a tree were exactly the same, could not
escape observation: small deviations of the same kind were met with
everywhere, among individuals as well as among the organs of the same
plant. Larger aberrations, spoken of as monstrosities, were for a long
time regarded as lying outside the range of ordinary phenomena. A special
branch of inquiry, that of Teratology, was devoted to them, but it
constituted a science by itself, sometimes connected with morphology, but
having scarcely any bearing on the processes of evolution and heredity.