> material, and comparing his views in detail with other theories. Darwin,

he says, had already distinguished between variability and mutability; the

former manifesting itself in gradual and isolated changes, the latter in

saltatory changes on a larger scale. The mistake made by Wallace and by

the later Darwinians has been that they regarded this latter form ("single

variation") as unimportant and not affecting evolution, and the former as

the real method of evolutionary process. That fluctuating individual

variations do occur De Vries admits, but only within narrow limits, never

overstepping the type of the species. Here De Vries utilises the recent

statistical investigations into the phenomena of individual variation and

their laws, as formulated chiefly by Quetelet and Bateson, which were

unknown to Darwin and the earlier Darwinians. The actual transition from

"species to species" is made suddenly, by mutation, not through variation.

And the state of equilibrium thus reached is such a relatively stable one

that individual variations can only take place within its limits, but can

in no way disturb it.



De Vries marshals a series of facts which present insurmountable

difficulties to the Darwinian theory, but afford corroboration of the

Mutation theory. In particular, he brings forward, from his years of

experiment and horticultural observation, comprehensive evidence of the

mutational origin of new species from old ones by leaps, and this not in

long-past geological times, but in the course of a human life and before

our very eyes. The main importance of the book lies in the record of these

experiments and observations, rather than in the theory as such, for the

way had been paved for it by other workers.



In contrast to Darwinism, De Vries states the case for "Halmatogenesis"

(saltatory evolution) and "Heterogenesis" (the production of forms unlike

the parents), taking his examples from the plant world, but his attitude

to Darwinism is conciliatory throughout. Eimer, on the other hand, is

sharply antagonistic, especially to Weismann; he takes his proofs from the

animal kingdom, and in the second volume of his large work already

mentioned, which deals with the "orthogenesis of butterflies," he attempts

to set against the Darwinism "chance theory," a proof of "definitely

directed evolution," and therefore of the "insufficiency of natural

selection in the formation of species."