67 
able. So, indeed, it was in his time; but later knowledge has 
thrown some light on the subject by showing that there are two 
kinds of variability to be reckoned with — namely, the deviations 
of the individuals of a species, or a variety, from the average char- 
acters of their groups— correctly termed by Darwin “ fortuit- 
ous’’—and the differences between species and varieties due to 
the oul or loss of characters. The first-named mode of 
variation is now distinguished as “ fluctuation’’ and it can be 
shown by ee calculation to be subject to the law of 
chance, as was supposed by Darwin. It was the products of this 
kind of variability upon which Darwin assumed that natural selec- 
tion must work in order to build up the characters of a new 
species. But Professor Hugo de Vries was not satisfied with 
Darwin’s assumption, and therefore took up the matter at this 
point and subjected it to scientific scrutiny. The results of his 
many years of research and experimentation have been set forth 
in his monumental work ‘ Die Mutationstheorie,”’ of which the 
book before us may be considered in part a summary, and in part 
pplement. Although the author claims that i work is ‘tin 
fall. pees with the oan laid down by Darwin,’’ he contends 
that there is no evidence that a species ever sroinaea by the ac- 
cumulation of “fluctuations ’ and undertakes to show that the 
only method by which one species can originate from another is 
by the sudden acquisition of a character or characters springing 
into existence fully formed, and completely hereditable— by a 
process called mutation. 
As a consequence of the far-reaching importance of Darwin's 
theories, many of his followers have been carried away by the 
allurements of deduction, and have been writing essays in support 
of evolution, when they ought to have been adding knowledge to 
hat Darwin accumulated. Professor de Vries is one of the few 
men of science who have undertaken to bring the great question 
which Darwin propounded, as to the derivation of species, back 
into the realm of observation and experiment. He is, in fact, the 
first who has advanced the matter much beyond the point at which 
Darwin left it. This he has accomplished by three methods of 
procedure: first, by traversing the history of botany, particularly 
