REVIEWS. 
87 
use? Complete reduction of leaf surface, for example, is obviously a 
useful character in the adaptation of plants to withstand a desert climate, 
but in what way small, almost inappreciable, amounts in such reduction of 
surface could serve the plant in its struggle against drought and enable it 
to persist is impossible to conceive. 
Again there are no transitional forms between the different species of 
plants. Those who seek “ connecting links ” do not adequately compre¬ 
hend the problem. But whereas species are discontinuous, environment 
is continuous. If fluctuations, a function of environment, had furnished 
the material for natural selection, then species ought to be continuous. 
Gradations, or “ connecting links,” would be abundant. 
The enormous length of time required to bring about the present con¬ 
dition by the selection of individual variations is another obstacle to their 
acceptance as the materials of natural selection. 
Darwin was less blind to these difficulties than some of his ardent 
followers have been, and in the latter editions of the Origin recognized 
that he had too greatly neglected discontinuous (“ spontaneous,” as he 
called it) variation. 
The importance of correct views as to the material upon which natural 
selection works is paramount for, as Bateson* has well said, “ Variation 
. . . is evolution,” while natural selection acts as a directing and con¬ 
serving force. 
The all importance of discontinuous variation as at least one method 
of the evolution of plants is emphasized and elaborated under the term 
Mutation by deVries in Die Mutationstheorie (Vol. I, 1901, Vol. II, 
1903). Most of the objections to the natural selection of individual 
variations as the manner of origin of species can not be urged against 
the mutation theory. Most important of all for science this theory is 
capable of experimental demonstration. One of the weighty objections 
to “ Darwinism ” was that no one had ever seen a new species arise and 
never could do so. This deVries has done and the experiment may be 
repeated by any one at any time with the requisite care and skill. His 
“ work claims to be in full accord with the principles laid down by Darwin, 
and to give a thorough and sharp analysis of some of the ideas of varia¬ 
bility, inheritance, selection and mutation, which were necessarily vague 
at his time.” t 
The present volume comprises the lectures delivered by the author at 
the University of California during the summer of 1904. It is not a 
translation or abridgment of the Mutationstheorie , but quite a new 
volume, and the author has “ tried to devote attention to the more 
important phases of the subject,” and has “avoided the details of lesser 
interest to the general reader.” The editor, Dr. D. T. MacDougal, of the 
New York Botanical Garden, is undoubtedly the best qualified for the task 
of any one in this country, having repeated deVries’ experiments, con- 
* Bateson, Materials for the Study of Variation, p. 6. New York, 1904. 
t deVries, Species and Varieties, p. ix. 
