224 BOTANICAL GAZETTE [MARCH 
Naturally the great problems of the cereal rusts receive considerable 
attention. Regarding the continuation of the rust through the agency of the 
seed, and Eriksson’s “mycoplasm”’ theory, the arguments are fully pre- 
sented, but the author regards these assumptions far from proved. 
The chapter upon methods of investigation is especially interesting and 
helpful. No one has done more or better work in this line of research than 
the author, and he speaks with long experience and wide knowledge. Six- 
teen pages are devoted to the study of rust problems from the point of view 
of plant geography, a subject that will grow more and more important as 
fuller data become available. In taking up the matter of the association of 
the host plants selected by the aecidial and teleutosporic generations, the 
author has developed a number of exceedingly ingenious and helpful charts. 
The seventy-five pages remaining of the first half of the book are devoted 
to the absorbing and intricate problems presented by specialization, the lim- 
itations of species and races, the origin of heteroecism, and the questions of 
sexuality. The numerous theories and facts are clearly and ably presented, 
but one must confess a feeling of disappointment that, after mastering 
present knowledge and canvassing the views of other writers, no sub- 
‘stantial advance is made in formulating an explanation of the problems. It 
is evident that these questions must await the writer who is a philosopher as 
well as a scholar, ; 
The second half of the volume is devoted to a detailed account of the 150 
or more species that have been studied by cultural methods. An index of 
species, one of hosts, and a full bibliography complete one of the most impor- 
tant contributions to the study of plant rusts ever published. —J. C. ARTHUR. 
Physical chemistry. 
STUDENTS and research workers in plant as well as in animal physiology 
will find Fischer’s translation of Cohen’s Physical Chemistry? an almost 
indispensable book. This treatise presents those considerations of the gen- 
eral subject which have a close bearing upon physiological phenomena, and 
presents them in a concise, clear, readable form, with only as much mathe- 
matics as is necessary for the establishment of the principles. Besides bsee 
physical chemistry, the book contains a discussion of a number of applica- 
tions of this science in hygiene, pharmacology, physiology, etc.— discussions 
_ which should be eye-openers to many’a student of biology. The subject-matter 
is divided into seventeen lectures, which are numbered serially. A seit! 
ment of their titles is given here to show the scope of the book: Reaction 
velocity ; Inversion of cane sugar and catalysis in general; The action baer ¢ 
ments; Temperature and reaction velocity; Equilibrium (three lectures); 
The friction of liquids; Osmotic pressure; The determination of the mo ss 
ular weight of dissolved substances; The theory of electrolytic dissocia- 
*COHEN, Ernst, Physical chemistry for physicians and biologists, translated by 
Martin H, Fischer. pp. viii +343. figs. ¢9. New York: Henry Holt & Co. 1903. 
