TIMIRIAZEFF'S RESEARCHES. 313 



one, or thirty per cent of carbonic acid, and made of red, 3'ellow, 

 green, blue, violet, and colorless glass. His results agree in 

 general with those obtained b}' the other methods. 



830. In 1870 further investigations in the same subject were 

 made b}' Pfeffer. 1 The following is a resume of the results of 

 his experiments with the leaves of five different plants exposed 

 to colored light : Only the visible rays of the spectrum cause 

 decomposition of carbonic acid ; and in this process the brightest, 

 that is, the yellow rays, are as efficient as all the others taken to- 

 gether, while the most refrangible rays, those which act most en- 

 ergetically upon chloride of silver, have only veiy slight influence 

 upon the work of assimilation. 



Every color of the spectrum ma}' be said to possess a specific 

 quantitative influence upon assimilation. This influence remains 

 unchanged whether the color is isolated, combined with one, or 

 with all the other colors of the spectrum when it acts upon a 

 part of a plant containing chlorophyll. 



831. Examination of the spectrum of chlorophyll (779) shows 

 that the part of the spectrum which absorbs most of the rays is 

 that which is pre-eminently its chemical end ; but by all the ob- 

 servers whose results have been cited in the text, it is held that 

 the chemical end is that which is least efficient in assimilation. 

 With the exception of the narrow though strong absorption-band 

 in the red, all the deep absorption-bands of chlorophyll and its 

 solutions belong at the violet or chemical end of the spectrum. 

 Miiller and Timiriazeff, cited in the notes, have endeavored to 

 investigate this anomaly. 



832. Timiriazeff,' 2 in a series of researches in 1877, experi- 

 mented upon the slender leaves of Bamboo, which he placed 

 in tubes of small calibre containing air of known composition, 



1 Arbeiten des botan. Inst. in Wiirzburg, 1871, p. 1. 

 The following works may also be cited : 



A. von Wolkoff, Einige Untersuchungen liber die "Wirkung des Lichtes von 

 verschiedener Intensitat auf die Ausscheidung der Gase durch Wasserpflanzen. 

 Pringsh. Jahrb., v., 1866, p. 1. 



Adolf Mayer, Production von organischer Pflanzen-Substanz bei Ausschluss 

 der chemischen Lichtstrahlen, Versuchs-Stationen, ix., ]867, p. 396. 



N. J. C. Miiller, Untersuchungen iiber die Diffusion der atmospharischen 

 Gase in der Pflanze nnd die Gasausscheidung unter verscliiedenen Beleucht 

 ungsbedingungen, Pringsh. Jahrb., vi., 1867, 478 ; and vii., 1869, 145. 



Timiriazeff, Botanische Zeitung, 1869, p. 169. 



Prillieux, Ann. des Sc. nat., ser. 5, tome x., 1869, p. 305. 



Baranetzky, Botanische Zeitung, 1871, p. 193. 



2 Annales de Chimie et de Physique, ser. 5, tome xii., 1877, p. 355. 



