512 SCIENCE PROGRESS 



examination of the products of assimilation. The work under review falls in the 

 third of the three categories mentioned. In his preface the author states that 

 before a rational discussion of the manner in which sugars are formed in the 

 green leaf is possible a clearer understanding of the conditions governing the 

 equilibria and mutual transformations of the carbohydrates of the leaf is necessary. 

 To this end he has attempted to determine the carbohydrates of cacti and 

 to examine the transformations these carbohydrates undergo under various 

 conditions. 



In the first chapter there is a very stimulating discussion on the transformations 

 that sugars undergo in vitro under various conditions, and the bearing of the facts 

 examined on the problems in the plant. The author then proceeds to describe 

 his experimental methods. These have evidently been worked out with great 

 care, and, when one remembers the difficulties always associated with the 

 determination of a number of substances of similar properties in presence of cne 

 another, one must congratulate the author on the measure of success that has 

 attended his efforts. 



The application of these methods has shown the presence in cacti of pentoses, 

 monosaccharide hexoses, disaccharides, pentosans, and polysaccharide hexoses. 

 The various quantities of these substances were determined in cacti at different 

 seasons and under different experimental conditions ; a further analysis of the 

 carbohydrates was not attempted. The general conclusions drawn are that low 

 water content and high temperature are associated with relative increase of 

 polysaccharides and pentosans and decrease of monosaccharides, while high 

 water content and lower temperatures are associated with relative increase of 

 monosaccharides and relative decrease of the more complex pentosans and 

 polysaccharides. 



Some observations were also made on aerobic and anaerobic respiration of 

 cacti. Under both conditions carbohydrates are consumed. In the course of 

 normal respiration in the dark there is a large production of malic acid as a 

 result of the restricted oxygen supply in these plants ; the alcohol production is, 

 however, small. During illumination the malic acid is disintegrated to carbon 

 dioxide and ethyl alcohol, the latter accumulating. Under anaerobic conditions 

 little acid is produced, but, on the other hand, large quantities of alcohol. 



The work concludes with a short discussion on the origin and role of pentose 

 sugars. The author appears to regard these as probably derived from more 

 complex sugars through glucuronic acid, which is present in cacti and which 

 should undergo photolysis in light into /-xylose and carbon dioxide in the same 

 way that malic acid gives ethyl alcohol and carbon dioxide. 



This work appears to be a sound and reliable contribution to our knowledge 

 of plant metabolism, and it is to be hoped the author will continue the prosecution 

 of his' researches into the chemistry of carbon assimilation. 



W. S. 



Botany for Agricultural Students. By John N. Martin, Professor of Botany 

 at the Iowa State College of Agriculture and Mechanic Arts. [Pp. x + 585.] 

 (New York : John Wiley & Sons ; London : Chapman & Hall, 1919. 

 Price \\s. bd. net.) 



In this book the fundamental principles of botany are set out and related to 

 subjects of economic importance such as agriculture, horticulture and forestry. 



