120 
REVIEWS. 
REVIEWS." 
T§ie Origin off Species by Mutation. 
[Die Mutations -theorie ; Hugo de Vries, vol. I., Leipzig, 1901.] 
This book brings together the results of many years’ labour devoted 
to subjects connected with the origin of species. The author brings 
forward a series of conclusions supplementary to Darwin’s memorable 
works, and developed along a line which has diverged widely from that 
followed by the recent school of mathematical evolutionists. These 
experiments and the doctrines based upon them possess so unusual a 
degree of interest that it appears worth while to try to give a short 
account of them which will be intelligible to a Ceylon public. It is 
much to be hoped that before long an English translation will place the 
whole work within the reach of those who do not read the German 
language easily. 
The second volume of this work, which has since appeared, deals 
mainly with experiments upon the crossing of various races of plants ; 
in the present article we are concerned only with the first volume. 
Since Darwin established the importance of the struggle for exis¬ 
tence, by reason of which weaker varieties die out and the stronger 
survive, the importance of a careful examination of the phenomena 
included by him under the head of variation has come to be recognized. 
In some writings upon this subject a confusion has arisen between the 
fact of the existence of varieties on the one hand and the process of varia¬ 
tion to which they owe their origin on the other; in order to understand 
the problem of how species arise it is necessary to keep the two clearly 
distinct. As to the process by which varieties arise, two methods 
appear at first sight to be possible. One of these is by the gradual 
accumulation of individual differences, i.e., such differences as occur 
normally among the several members of a family. This is known as 
the continuous method of origin of new forms, and takes place by the 
steady aggregation of differences occurring in the ordinary course of 
normal variability. Or, on the other hand, a new variety may appear 
discontinuously , at a single step ; the new form differing from its parent 
to a clearly recognizable extent, and showing no tendency in its 
offspring to “ revert” to the parental type. An extreme case of this 
process is the appearance of “ sports” and of the still more “ abnormal ” 
forms known as “monstrosities.” De Vries applies the term mutation 
to this discontinuous method of origin of varieties or sub-species. 
* Written for the Ceylon constituency of this journal, and dealing with 
advances in science of local interest. 
