OTHER CARBON COMPOUNDS 327 



monoxide nor marsh gas (CH 4 ) can be assimilated either alone or in the 

 presence of carbon dioxide 1 . Carbon monoxide acts as a violent poison 

 only to those organisms which contain haemoglobin, and in all other cases 

 it behaves almost as a neutral gas, so that it is very much less poisonous 

 to plants than the dioxide. 



In plants of the Crassulaceae and various other green succulents, the 

 free organic acids (malic, isomalic, and oxalic) produced during the night 

 are decomposed in light with an evolution of oxygen, and a production of 

 carbohydrates (starch, &c.) ' 2 . Apparently the organic acid undergoes 

 further oxidation under the action of light, the carbon dioxide produced 

 being immediately assimilated, for in non-chlorophyllous plants the organic 

 acid produced at night-time may undergo similar oxidation, although as 

 a general rule the amount of acid formed is comparatively small, and 

 hence the daily variations in the acidity of the tissues are but slight 

 or imperceptible. It is of great importance to fleshy plants that as 

 little carbon dioxide should be lost during the night as possible, and 

 that it should be preserved in the form of non-volatile organic acids 

 for assimilation during daytime, for in these plants gaseous exchange is 

 difficult and a sufficient supply of carbon dioxide is hard to obtain 3 . 



Malic, oxalic acids, &c. are actually decomposed with an evolution 

 of carbon dioxide when light acts upon them in the presence of certain 

 substances, and living plant-tissues appear to act in a similar manner in 

 accelerating such decomposition 4 , for chlorophyllous plants may evolve 

 oxygen at the expense of organic acids which surround the plant in solu- 

 tion, or which have been injected into it 5 . 



1 Saussure, Rech. chim., 1804, p. 208; Boussingault, Agron., Chim. agric., &c., 1868, T. IV, 

 p. 300; Stutzer, Ber.d. Chem. Ges., 1876, Bd. ix, p. 1570 ; Just Forsch. a. d. Geb. d. Agriculturphys., 

 1882, Bd. V, p. 79. On CH 4 , Boussingault, 1. c., p. 300. 



2 Literature : Ad. Meyer, Versuchsst., 1875, Bd. xvm, p. 410; 1878, Bd. xxi, p. 277 ; 1884, 

 Bd. XXX, p. 217; 1887, Bd. xxxiv, p. 127; Die Saueibtoffabscheidung fleischiger Pflanzen, 1876; 

 G. Kraus, Uber die Wasservertheilung in der Pflanze, IV, 1884, and Stoffwechsel bei den Crassulaceen, 

 1886 (Sep.-abdr. a. d. Abhandlungen d. Nat.-Ges. z. Halle, Bd. XVI) ; H. de Vries, Periodicitat im 

 Sauregehalt d. Fettpfknzen, 1884 (Sep.-abdr. a. Meded. d. Akad. in Amsterdam) ; Warburg, Unters. 

 a. d. Bot. Inst. z. Tubingen, 1886, Bd. II, p. 53; Aubert, Rev. gen. d. Bot., 1892, Bd. IV, p. 203, and 

 Ann. d. sci. nat., 1892, vii. ser., T XVI, p. I ; Purjewicz, Bot. Centralbl., 1894, Bd. LVHI, p. 368. 



3 Cf. Warburg, 1. c. ; A. Meyer, 1. c., 1887, p. 140. 



* Becquerel, La lumiere, 1868, T. II, p. 60; Ar. Miiller, Einfluss d. Lichtes auf Wasser, 1874, 

 p. 25; Ad. Mayer, I.e., 1878, p. 321 ; de Vries, I.e., 1884, p. 53." Purjewicz, I.e., 1894, p. 371; 

 Wehmer, Bot. Zeitung, 1891 , p. 322 ; Richardson, Ber. d. Cbem. Ges., 1894, Ref. p. 496. A solution 

 containing Fe 2 Cl 6 and oxalic acid evolves CO 2 actively in sunlight. Cf. also Ostwald, Lehrb. d. 

 allgem. Chemie, 1893, Bd. II, p. 1031. 



5 Warburg, 1. c., 1886, p. 112 ; Mangin, Compt. rend., 1889, T. cix, p. 716. Schmdger (Ber. 

 d. Chem. Ges., 1879, Bd. Xll, p. 373) has shown that the increase in the dry weight, which Stutzer 

 (Versuchsst., 1877, Bd. xxi, p. 93) observed in plants fed with organic acids, is due to the assimi- 

 lation of CO 2 derived from these acids. Since the decomposition of the acid takes place only under 

 certain conditions, negative results may be obtained in some cases. See Ad. Mayer, Versuchsst., 

 1884, Bd. xxx, p. 226. Wehmer, indeed, finds that the formation of citric acid in Citromycts is not 



