Nd 
LOTSY, CURRENT THEORIES OF EVOLUTION. 405 
to apply to variability to explain the existence of this diversity, 
that even MENDEL’s work was not able to lead us away from the 
road of variability. 
I well remember how on a walk during a beautiful summerday 
in the Thuringian mountains, now some 10 years ago, the idea forced 
itself upon me: transmittable variability does not exist, all what 
has been described as such was either diversity within a group 
of individuals, erroneously considered to be of the same genotype, 
or segregation from heterozygotes, erroneously considered to be 
homozygous. 
Nobody is responsible for his thoughts, nor deserves either credit- 
or blame for them, but it is the duty of the scientist to follow 
them up and to test their value. This I have done ever since. 
At the time the thought occurred to me, a notable objection 
offered itself at once: varieties were supposed to differ funda- 

mentally from species. Hybrids between varieties were generally 
supposed to segregate; such between species to be constant. 

Yet, CORRENS, experiments with Mirabilis and Baur’s and my 
own with Antirrhinum had already shown that this could not be 
a general rule and we now know, that we cannot distinguish 
varieties from species by crossing. 
What then, if transmittale variability should not exist, if the 
genotype were immutable by itself, could be the cause of change 
and consequently of Evolution? ; 
The remarkable diversity which the Fy of a cross between 
Antirrhinum majus and A. glutinosum showed, induced me to 
consider hybridization as the cause of change and made me put 
forward the theory of evolution by means of hybridization. 
That the diversity so obtainable is enormous and far surpassed 
anything that had ever been imagined on a basis of variability 
there is no doubt. That the simultaneous production of so large 
a number of different forms offered a much better chance to na- 
tural selection than a few sports could possibly do, there could 
be no doubt either, while it had already been proved by DE 
Vries that the so called continuous or fluctuating variations were 
_nothing but modifications. | therefore felt and still feel, that if 
DARWIN had known of the great diversity caused by a cross, he 
would certainly have considered these diverse forms, arisen simul- 

