timiriazeff's researches. 313 



one, or thifty per eont oC earlioiiic iicid, and made of red, j-ellow, 

 green, bluL', violet, and colorless glass. His results agree in 

 general with tliose obtained by tlie other methods. 



830. In 1870 further investigations in tlie same subject were 

 made by Pfeffer.^ The following is a resume of the results of 

 his experiments witli the leaves of five different plants exposed 

 to colored liglit : 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 effleicnt as all the others taken to- 

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

 ergetically upon chloride of silver, have ouh' very slight influence 

 upon the work of assimilation. 



Every color of the spectrum may be said to possess a s|iecific 

 quantitative influence upon assimilation. This influence remains 

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

 with all the other coloi-s of the spectrum when it acts upon a 

 part of a plant containing chlorophyll. 



831. pjxaraination 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 tliough strong absorption-band 

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

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

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

 investigate this anomaly. 



832. Timiriazeff,^ 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 botun. Inst, in Wiirzburg, 1871, p. 1. 

 The following works may also be cited : — 



A. von AVolkoff, Einige Untersiichungen libei' die Wlrkung des Liohtes von 

 verschledener Intensitat auf die Ausscheidiing der Gase durch Wasserpflanzen. 

 Pringsh. Jalirb., v., 1866, p. 1. 



Adolf Mayer, Production von organischer Pflanzen-Substanz bei Ausscliluss 

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



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

 Gase in der Pflanze nnd die Gasausscheidung untev vevschiedenen Beleucht- 

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



Timiriazeff, Botaniache Zeitung, 1869, p. 169. 



Prillieux, Ann. des So. 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. 



