W. F. R. Weldon 
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rarely occur, and when they do an explanation is offered which removes them 
from the category of the other variations. Leaves with less than three leaflets are 
also rare. 
Since the race is now constant, Professor de Vries suggests that without a new 
mutation its character cannot be further changed. Experiments to test this 
supposition, which he has doubtless made, are not described. 
The result is of very great interest, but there is no scrap of evidence to show 
that any part of it is due to the remarkable form of regression to which it is 
ascribed. Professor de Vries has proceeded throughout his experiment as if 
Mr Galton's view of inheritance applied to the character selected, and the results 
obtained are in exact accordance (so far as they can be judged from the data given) 
with the truth of that view. 
The whole book is full of records of experiments as interesting and instructive 
as the record of work on Clover referred to ; especially a large part of it is devoted 
to the wonderful forms of Oenothera lamarkiana which Professor de Vries has 
raised. But I cannot find evidence that in any one of these numerous experi- 
ments the kind of regression ascribed to the offspring of mutations has actually 
occurred. 
The only difficulty in reconciling results, such as those obtained by Professor 
de Vries, with Darwin's theory of Natural Selection as it is commonly understood 
seems to me to arise from a belief that the operation of natural selection is of 
necessity slow, while many new races have certainly been established in a few years. 
In speaking of the possible slowness of selection in a wild state I think Darwin 
was influenced first by his constant desire to present his own theory in a way 
which should give the fullest opportunity for reasonable objection, and secondly by 
the perception that selection might often be indirect, and therefi^re fail to act so 
rigidly upon a particular character as the selection of a human breeder can act. 
He certainly realised that it can act very quickly under favourable conditions. 
The ease of artificial selection has been very fully discussed by Professor Pearson, 
on the basis of Mr Galton's work and his own, in his " Law of Ancestral 
Inheritance*," and it is shown that a view of regression essentially identical 
with that stated by Mr Gal ton (but not with that attributed to him by Professor 
de Vries) leads to the expectation that by selecting parents of constant character 
for some six or eight generations it will be possible to produce a race of offspring 
whose mean will closely approximate to that of the selected parents ; and further, 
that after some dozen generations of such selection, the mean character of race 
will be permanent. 
This result of Professor Pearson's is in complete accord with the experimental 
results obtained by Professor de Vries ; it is in complete accord with the little we 
know concerning the history of domestic races of animals and plants, but it 
* li. S. Fruc. XLii. p. 
