THE INFLUENCE OF LIGHT m 339 



or permanently inactive (Ewart, 1. c., p. 434). This is perhaps why certain 

 investigators have failed to detect any power of assimilating carbon dioxide 

 in plasmolysed plants l . 



Chloroform Ether. The direct and indirect effects of any agency 

 need carefully to be distinguished from one another; thus by prolonged 

 anaesthetization a chloroplastid may be rendered temporarily inactive, and 

 hence it is not always clear whether .the action of chloroform and ether is 

 a direct or indirect one. Fr, Schwarz and Pringsheim found that in strong 

 watery solutions of chloroform and ether assimilation soon ceased, but that 

 no recovery was possible owing to the plants having been fatally injured, 

 whereas Bonnier and Mangin showed that in an atmosphere containing 

 a measured quantity of ether, the assimilation of carbon dioxide was directly 

 inhibited, although respiration continued unchecked. By exposing plants 

 for prolonged periods of time to dilute ether vapour Ewart was able to 

 render the chloroplastids temporarily inactive 2 . 



Oxygen. In the absence of free external oxygen a normal chloroplastid 

 will continue to assimilate in an atmosphere of hydrogen containing a little 

 carbon dioxide. Even if no oxygen was originally present it may be shown 

 by the bacterium method that it is evolved as soon as light is admitted. 

 Beyerinck found that plants immersed in a solution of reduced indigo 

 evolved oxygen and caused the solution to turn blue when they were 

 exposed to light. Prolonged asphyxiation caused by a deficiency of 

 oxygen may, however, ultimately induce a condition of temporary or 

 permanent inanition in the chloroplastids during which they lose the 

 power of assimilating carbon dioxide 3 ; this was what Boussingault termed 

 ' asphyxie.' 



SECTION 59. The Influence of Light. 



Even the feeblest illumination renders the chloroplastids able to 

 decompose carbon dioxide, so that slightly less is given off than in absolute 

 darkness, but oxygen is evolved only when more carbon dioxide is decomposed 

 than is produced by respiration. Hence, even the delicate bacterium method 



1 The formation of starch alone is naturally not a sufficient test for the presence of a power of CO 2 - 

 assimilation (Sect. 55), and hence Meissner's results are inconclusive (Bot. Centralbl., 1894, Bd. LX, 

 p. 206), as are also those given by Weyl (Sitzungsb. d. Phys.-Med. Soc. zu Erlangen, i. Aug., 1881. 



2 Cl. Bernard's observations left it uncertain whether the action of the chloroform was a direct 

 or indirect one (Le9ons sur les phe"nomenes d. 1. vie, 1878, p. 278), and Ewart (Ann. of Bot. 1898, 

 Vol. XII, p. 416) has recently shown that the result produced differs according to the duration of the 

 exposure. Fr. Schwarz, Unters. a. d. Bot. Inst. z. Tubingen, 1881, Bd. I, p. 102; Pringsheim, 

 Sitzungsb. d. Akad. d. Wiss. zu Berlin, 1887, Ober die Abhangigkeit d. Assim. gr. Zellen von 

 Sauerstoffathmung ; Bonnier et Mangin, Ann. d. sci. nat., vii. se"r., T. Ill, 1886, p. 14; Jumelle, 

 Rev. ge"n. d. Bot., 1892, T. n, p. 430; Ewart, Journ. Linn. Soc., xxxi, 1896, p. 408. 



3 Pringsheim, I.e.; Ewart, I.e., pp. 403, 418, &c.; Beyerinck, Bot. Zeitung, 1890, p. 742. 



Z 2 



