126 
REVIEWS. 
was obtained, the majority of leaves of which had five lobes, whilst 
some had six or seven. Since, however, it appeared impossible to get rid 
by selection of a certain proportion of three-lobed leaves, or, on the other 
hand, to obtain leaves with more than seven lobes, De Vries regarded 
his experiment as showing the existence of a mid-race, and not of a 
constant race or true variety. 
Several of the views enforced in the present volume have long been 
familiar to practical breeders and gardeners, to whom this confirmation 
of their established practice will be all the more welcome, because 
recently a majority of authorities upon the subject of variation have 
held contrary opinions. Still more must this work be welcome to those 
engaged in scientific investigations bearing upon the subject of species. 
And the general public interested in evolution may welcome it as 
introducing, on the whole, decidedly simpler ideas of method, in spite 
of the amount of novelty which accompanies them. 
At the same time the originality of most of the work appears un¬ 
impeachable. As a connected argument, in which close reasoning and 
careful investigation are applied to the elucidation of a difficult biologi¬ 
cal problem, the book deserves comparison with that well-known 
model of these qualities, the Origin of Species. In scope it is more 
nearly comparable with that larger intended work, of which the Origin 
was only an abstract. The host of examples in which elemental 
spacies, between-races, and varieties are shown to exist and to be sepa¬ 
rable by selection is most striking. In no case has it been shown that 
such forms can be built up by the gradual selection of individual 
differences. Darwin was wont to say that'as soon as the slightest 
tendency to vary in a particular direction has appeared, the breeder can 
by selection produce a race in which the character is strongly marked. 
De Vries now shows that in such cases the slight tendency indicates 
the appearance of a minus-variation of a definite new form, which only 
requires isolation for a few generations in order to appear fully and 
typically developed. Natural selection is active in “ building up ” 
species into genera, sub-species into species ; it does not account for 
the differences between Jordan’s species ; and these are, in De Vries’s 
opinion, true physiological species. Of the origin of such species 
mutation gives us a suitable explanation ; it also explains the difficulty 
as to how characters of no use to a species or even actually disadvan¬ 
tageous may have arisen ; a point which is quite inexplicable upon the 
rival view. 
Many of De Vries’s experiments have been carried out at what isfor 
the subject lightning speed, and may require confirmation at a more 
wary pace. But it cannot be doubted that at the outset of a new 
century the writer has supplied a splendid starting-point for the 
progress of further studies in the origin of species, and that in the near 
future we may look for an even more marked advance. 
B. H. L. 
