BOOKS AND CUREENT LITERATURE 225 



stricted an application that it is of little value in biological calculations. 

 The assumptions made in its formation are also incompletely stated, 

 for they include, besides those enumerated, the requirement that the 

 vapor be a perfect gas. Although the attempt to put osmotic pressure 

 on a more rational basis than it has in biology at present is commend- 

 able, the author's space is entirely inadequate for this purpose. The 

 definition of osmotic pressure is incomplete, for it takes no account of 

 the quantitative difference in the effects of pressure upon the solvent 

 and the solution, and the discussion of the nature of osmosis leaves the 

 reader with the impression that there is must less definite information 

 on the subject than is actually the case.^ 



In his presentation the author has included a large amount of the 

 graphical and numerical results of the researches considered. About 

 these results he has built the discussion, which consists chiefly of a 

 critical comparison of the conclusions and opinions of the various in- 

 vestigators, and this necessitates in many cases a consideration of the 

 methods employed. The point of view throughout is that of the ex- 

 perimentor and little attention is paid to the effect of these results 

 upon the more general aspects of plant physiology. 



The discussion is excellent and by its very form should stimulate 

 students who are attempting to acquire a power of critical comparison 

 of experimental results, although the author at times employs expres- 

 sions that seem to strengthen an argument beyond its proved value. 

 This overstatement appears to be due to a desire not to undervalue 

 results whose experimental details he does not undertake to criticize, 

 for in the fields in which he has worked his statements are less emphatic. 

 The criticisms of methods are usually judicial and are a valuable feature 

 of the book. Unfortunately the physics or chemistry underlying the 

 methods is at times overlooked, and, in his desire not to undervalue, 

 the author occasionally seems to overvalue. 



The book is well written, very readable and well arranged, and it is 

 to be hoped that its reception will stimulate the presentation of other 

 phases of plant physiology in a similar manner. — H. E. Pulling. 



Prothallia of Lycopodium. — An interesting and important botani- 

 cal discovery — that of the fh'st prothallia of Lycopodium to be found in 



2 One of the best accounts of the present state of knowledge on this subject 

 and that of osmotic pressure is to be found in Washburn's Physical Chemistry 

 (Washburn, Edward W., An Introduction to the Principles of Physical Chemistry. 

 New York, 1915). 



