RECENT ADVANCES IN SCIENCE 225 



Willstatter and collaborators, whose important work on 

 the chemistry of the pigments of the green leaf has attracted 

 world-wide attention, have followed up this work by investiga- 

 tions on the physiological aspect of chlorophyll in a series of 

 preliminary papers. (R. Willstatter and A. Stoll, (1) " t)ber die 

 chemischen Einrichtungen des Assimilationsapparates," Sit- 

 zungsb. d. k. Preuss. Akad. der Wiss., 191$, 322-46; (2) 

 " Uber die Assimilation ergriinender Blatten," Sitzungsb. d. k. 

 Preuss. Akad. der Wiss., 191 5, 524-32; (3) " Untersuchungen 

 liber die Assimilation der Kohlensaure (Erste vorlaufige Mittei- 

 lung) : Uber die Beziehungen zwischen Chlorophyllgehalt und 

 assimilatorischer Leistung der Blatter," Ber d. deutsch. chem. 

 Ges. 48, 1540-64, 191 5). 



Willstatter 's investigations have been carried out much on 

 the same lines as the extensive researches of F. F. Blackman 

 and H. T. Brown in this country, but with the improvement that, 

 besides determining the quantitative relations of carbon 

 dioxide, temperature and illumination as these authors have 

 done, the amount of chlorophyll is estimated quantitatively 

 by the refined and accurate methods published by Willstatter 

 in earlier papers. Assuming with F. F. Blackman that the 

 principle of limiting factors is valid for the processes of carbon 

 assimilation he uses a high concentration of carbon dioxide 

 (5 per cent.), a moderately high temperature (25 C.) and high 

 light-intensity (a 3,000 candle-power Osram lamp at distances 

 varying from 15 to 35 cm. from the leaf chamber). Under 

 these conditions neither light nor carbon dioxide is a limit- 

 ing factor. The amount of carbon dioxide assimilated can 

 then only depend on internal factors and the temperature. 



Willstatter varied the chlorophyll content by choosing 

 leaves in different stages of development ; spring, summer and 

 autumn leaves, leaves poor in chlorophyll (yellow varieties), 

 etiolated leaves and chlorotic leaves. 



The first important point brought out is that the assimila- 

 tion number (the ratio between the amount of carbon dioxide 

 assimilated per hour and the amount of chlorophyll) is not 

 constant, thus disclosing that other internal factors come into 

 play. A study of the influence of temperature and light on the 

 assimilation of leaves of green and yellow varieties of the same 

 species convinced Willstatter that carbon-assimilation consists 

 of two processes, a photochemical process and an enzymatic 



