392 LOTSY, CURRENT THEORIES OF EVOLUTION. 
This conception of the immutability of JoRDAN’s species or of 
pure lines, or, as we would now express it, the immutability of the 
homozygous as well as of the haploid genotype, was of course utterly 
distastefull to evolutionists, who could conceive of no other pos- 
sibility of evolution, than by some process of variability and, asa 
consequence,’ JORDAN’s splendid work was disregarded. 
All the same, [ feel inclined to believe that JORDAN was right, 
that the pure genotype is immutable; anyhow there is no doubt, 
that the cases of transmittable variability mentioned by LAMARCK 
and DARWIN were nothing of the kind, but were either modifications, 
wrongly supposed to be able to become transmittable or diversities 
within groups of individuals, wrongly supposed to be homogenous 
or, again, segregates from heterozygotes, wrongly supposed to be 
homozygotes. 
The new period of evolution begins with DE VRIES. 
JORDAN’S work was, as we saw, disregarded; the existence of 
transmittable variability had become a dogma, and in stead of 
experimenting one limited ones efforts to discussing which kind 
of variability was the cause of evolution. 
We all know that DE Vries claimed to have proved the existence 
of mutation in the case of Oenothera Lamarckiana. 
It is a curious fact that this claim, at the time it was presented, 
was very generally granted, because DE VRIES himself stated, that 
he had never possessed a Lamarckiana which did not throw the 
aberrant forms, which he called mutants, so that all he actually 
proved — a very important fact — is that O. Lamarckiana was a 
type of plant which throws aberrant forms in every generation. 
This of course made the mutational nature of these aberrant forms 
purely hypothetical and forced DE VRIES to place their origin in 
the uncontrollable past. 
The very curious behaviour of O. Zamarckiana, discovered by DE 
VRIES, has not yet been entirely elucidated; different investigators 
offer different explanations but all agree, and even DE VRIES has 
admitted, that the Lamarckiana’s, which we actually know are hete- 
rozygotes, while it has also been proved that a considerable part 
of DE Vries’ socalled mutants are certainly not due to mutation 
but to irregular chromosome distribution. 
Not all however; and this puts us under the obligation to consider 







