228 BOTANICAL GAZETTE [SEPTEMBER 
tary forms—whether “elementary species” or ‘“‘varieties” in the DeVriesian 
sense—he has proposed the convenient term biotypes. He also distinguishes 
them as genotypes, that is, collections of individuals having like germinal 
characters to distinguish them from mixtures of individuals having like external 
characters, but of unlike germinal composition. To these latter mixtures, 
whose uniformity is only apparent, he gives the name phenotypes. 
Heredity is recognized as only one of many factors involved in evolution, 
and the author does not even attempt to enumerate the other factors, discuss- 
ing briefly only such other evolutionary factors as are directly related to the 
question of permanence of types, for example, natural selection, Weismannism, 
direct influence of environment, inheritance of acquired characters, etc. He 
dismisses all which are not based upon a clear distinction between the different 
kinds of variation and the different kinds of types as purely speculative, and 
€ 
mutation and hybridization, these subjects are treated in a very satisfactory 
manner. It is impossible in so short a space nearly to cover these fields in 
detail, and the method used is the same as in the biometrical part of the book, 
appropriate examples being introduced to illustrate each phase of the subject, 
no attempt being made to give a comprehensive account of the many invest 
tions which have been made. With a detailed account of the recent work in 
Mendelian heredity, we are fortunately supplied at the present time by BATE- 
SON’S most recent book? on the subject, which, together with this book by 
JOHANNSEN, gives us a practically complete discussion of what has been done 
in the study of heredity by exact scientific methods. 
While JouannseEn’s book is written in German, and is therefore less acces 
sible to the entire English-reading public than might be wished, he has fortunately 
written with great simplicity and directness, and thus his work is more easily 
read than is often the case. The author has been criticized by German reviewer? 
: sh idiom, 
which is more nearly like the English; consequently, his book is more y 
closely. The value of the work is greatly enhanced by the fact that the author’ 
discussions are illustrated at every point by detailed examples from his ow? 
incisive experiments. It is, therefore, a treasure-trove of neW knowlert 
leading to conclusions which are certain to have a large place in the future 
* Bateson, W., Mendel’s principles of heredity. pp. xiv+39°- pis. 6. fits T 
Cambridge: University Press. 1 
