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BOTANICAL GAZETTE 



respond with the similar European forms. This attitude appears to be of 

 very dubious value indeed, in view of the completeness of the agreement never 

 before questioned between the American genera and even species and those 

 of Europe as long recognized by distinguished students of both floras . This 

 position in regard to American supposed mesozoic sequoias and their European 

 counterparts is not the less surprising in view of the meagerness and bad state 

 of preservation of her material, in contrast to the abundance and perfection of 

 that from American deposits. 



The volume closes with anatomical descriptions of the woody dicotyledon- 

 ous genera Cantia, Woburnia, Sabulia, Hythia, and Aptiana, which present no 

 feature of interest beyond vouching anatomically for the presence of the dicoty- 

 ledons in the early Cretaceous.— E. C. Jeffrey. 



Michaelis 2 is the author of the first of a series of Monographs on plant 

 and animal physiology. The series, which is edited by Czarek and Parnas, 

 is to bear somewhat the same relation to its realm as the well known Mono- 

 graphs on biochemistry bear to their more restricted field. Many of the pro- 

 posed numbers promise to be of the greatest interest to plant physiologists. 

 The present volume deals with hydrogen ion concentration, its significance 

 in biology, and the methods for measuring it. In the introduction the author 

 points out the importance of the "actual " reaction of the medium in determin- 

 ing the course of chemical changes in organisms, and cites instances of the 

 misinterpretation of experimental results due to failure to consider this factor. 



The monograph is divided into three parts. In the first the theoretical 

 significance of hydrogen ion concentration is discussed. Following a develop- 

 ment of the general principles and formulae for the dissociation of water, acids 

 and bases, and amphoteric electrolytes, these are applied to the special cases 

 of proteins and enzymes. By combining the results of experiments on the 

 influence of hydrogen ion concentration on enzyme activity, and the results 

 of transfer experiments on the same enzymes, some interesting conclusions are 

 drawn as to the chemical nature of the enzymes studied. Invertase, for 

 instance, is considered an amphoteric electrolyte of which only the undis- 

 sociated part of the "invertase acid" is effective, and only the cations of pepsin 

 are effective in hydrolyzing proteins. 



The second part of the monograph is a statement of present knowledge 

 as to the hydrogen ion concentration at which physiological processes go on 

 in organisms, the variations of this factor that occur, and the means the organ- 

 ism possesses for regulating the acidity of its body fluids. In general, if a 

 body fluid is characterized by a specific enzyme, the hydrogen ion concentration 

 of the fluid corresponds to the optimum for that enzyme. The variations are 



3 Michaelis, L., Die Wasserstoffionenkonzentration, ihre Bedeutung fur die 

 Biologie und die Methoden ihrer Messung. Berlin. 1914. 



