RECENT ADVANCES IN SCIENCE 227 



of simple chemical reactions than was formerly the case. Thus, 

 for instance, the formaldehyde hypothesis of carbon assimila- 

 tion seems at last to have lost the prominent position it has so 

 unworthily occupied for nearly half a century. H. A. Spoehr 

 (" Theories of Photosynthesis in the Light of some new Facts," 

 The Plant World, 19, 1-16, 1916) has published a carefully 

 reasoned criticism of this theory, particularly in regard to the 

 formation of formaldehyde from carbon dioxide and water 

 under various conditions. He shows that what evidence there 

 is could be used with much greater force in support of a formic 

 acid theory of carbon assimilation, but he does not consider that 

 the putting forward even of a formic acid theory would be at 

 all justifiable. Jorgensen and Kidd (" Some Photochemical 

 Experiments with Pure Chlorophyll and their Bearing on 

 Theories of Carbon Assimilation," Proc. Roy. Soc. B, 89, 342-61, 

 19 1 6) have repeated with pure chlorophyll the experiments 

 made by earlier investigators on the formation of formaldehyde 

 in a system consisting of chlorophyll, water and carbon dioxide 

 exposed to light. It was found that formaldehyde is only pro- 

 duced when oxygen is present, and then only as the result of a 

 thorough disintegration of the chlorophyll molecule. Further 

 criticism of the various theories of carbon assimilation and a 

 review of the whole subject is to be found in the monograph of 

 the subject by Jorgensen and Stiles (New Phytologist Reprint 

 No. 10, London, 191 7). 



An attempt to revive the old theory of Liebig and others 

 who supposed that organic acids were formed in carbon assimi- 

 lation, has recently been made by A. B. Steinmann (" Studien 

 iiber die Aziditat des Zellsaftes beim Rhabarber," Zeitsch. f. 

 Bot. 9, 1-59, 191 7). He has made a study of the acidity of the 

 cell-sap of leaves and leaf-stalks of Rheum, and shows that the 

 content of acid runs parallel to that of carbohydrate in the 

 organs of assimilation. He contends, therefore, that in an acid- 

 forming non-succulent plant like rhubarb, the acid is a product 

 of assimilation. 



The study of the products of assimilation in normal plants 

 has been made the subject of several recent researches. In 

 order to test and amplify the classical observations of Brown 

 and Morris on the distribution of the products of assimilation 

 in leaves, W. A. Davis, A. J. Daish and G. C. Sawyer have 

 made analyses of the carbohydrates in leaves of mangold 



