SPECIES AND VARIETIES 165 
one pages of introductory matter. The thirty-seven lectures which 
follow discuss in admirable detail the subject-matter under the five 
heads of elementary species, retrograde varieties, abil orting 
varieties, mutations, and, lastly, fluctuations. e fourth section, 
as might be expected, is the longest, and comprises ae thir d of the 
book.» The first mutation dealt with is that of ad sind Masti flax. 
been seen in the wild state. The only botanist who succeeded in 
sowing seeds of the peloric variety was Willdenow, and he obtained 
only very few seedlings. 
The author ee into the discussion on Mutation with all the 
enthusiasm of the neophyte. He gives the most lucid exposition of 
the theory which has yet been offered to philosophical biologists. 
0) 
convenient gaps. ” He eh earmarks the pieiontare i of Lord Kelvin 
and other physicists, in which Brig! endeavour to show that great 
limitations have to be put upon the enormous demands for time 
the gst. th on tipi ch the argument 
hinges is the of the secular cooling of the prude If Prof. 
ries, a6 tein launches mutations in the same boat with cata- 
author is inclined to throw cold water on the arguments of the 
mathematical biologists, such as Karl Pearson, Kapte 
at 
is, therefore, a concession to the claims of those who, like Wallace, 
restrict within hai limits the principles of evolution, limits 
never circumscribed y Darwin himself. He formulates, as a 
