THE NATURE OF PHOTOSYNTHESIS 171 



tives of these substances may play an important role in the formation of 

 organic compounds found in plants. 



Formaldehyde: This substance has played a xtvy important role 

 in the theoretical discussions of the photosynthetic process. The behavior 

 of plants toward formaldehyde is considered in Chapter 5. 



Anesthetics: The inhibiting efifect of chloroform on the photosyn- 

 thesis of aquatic plants was first described by Claude Bernard and has 

 been repeatedly verified. If the anesthetization is not continued too long 

 permanent injury to the chloroplasts can be avoided and they regain their 

 activity. Bonnier and Mangin,-"' like Bernard,-"* showed that photosyn- 

 thesis is more sensitive to the action of ether and chloroform than is 

 respiration and that by carefully regulating the quantities of these sub- 

 stances administered, a separation of the two processes can be attained. 

 Thus it is possible to stop photosynthesis and allow the respiration to con- 

 tinue. The separation is, however, not a very sharp one, for with the 

 amounts of ether or chloroform required to stop photosynthesis, the rate 

 of respiration is also afifected : either it is somewhat inhibited or with small 

 quantities of the anesthetic it is accelerated. Dift'erent species of plants 

 show a wide variation in their reaction to ether and chloroform. A thor- 

 ough investigation of the effect of anesthetics has been made by Irving. 

 From this it is apparent that small doses of chloroform affect the gaseous 

 exchange so that light produces little effect thereon. Very small concen- 

 trations of ether and chloroform exert a stimulating influence on respira- 

 tion, but it is very doubtful whether any such acceleration occurs in photo- 

 synthesis. From the investigations of Willstatter and Stoll it is apparent 

 that quantities of chloroform which inhibit the rate of photosynthesis 

 effect a decomposition of the chlorophyll in leaves of Prunus laurocerasus. 

 With ether, while recovery of the photosynthetic activity is not complete, 

 there is apparently no appreciable alteration in the chlorophyll and caroti- 

 noid components. 



Narcotics: morphine, cocaine, and quinine, inhibit photosynthesis. 

 Treboux reports a 0.005 per cent solution of quinine hydrochloride of 

 very slight effect, while a 0.15 per cent solution of the same salt inhibits 

 completely.-"^ Antipyrene is equally poisonous. Warburg has investi- 

 gated the effect of urethanes. The inhibiting action of a homologous 

 series depends apparently upon the absorption of these substances. Photo- 

 synthesis is far more sensitive to these substances than respiration. The 

 latter is stimulated by weak solutions, which inhibit photosynthesis. The 

 concentrations affecting respiration are about twenty times as strong as 

 those affecting photosynthesis. The following table from Warburg illus- 



*" Bonnier and Mangin, .hni. Sci. Xat. (7), 3, 14 (1886). Schwartz, Untcrs. a. 

 d. Bot. Inst. Tiibingcn, 1, 102 (1881). Ewart, Jour. Limican Soc, 31, 408 (1896). 

 Irving, Ann. Bot.. 25, 1077 (1911). Bose, "The Physiology of Photosynthesis," 

 London, 1924, p. 60. 



*" Bernard, "Legons sur les phenomenes de la vie," 1878, p. 278. 



^"Jacobi, Flora. 86, 323 (1899). Treboux, ibid.. 92, 56 (1903). Warburg, Bio- 

 chetn. Zeit., 100, 264 (1919); 103, 196 (1920). 



