526 RESPIRATION AND FERMENTATION 



de Saussure '. The former showed that all living tissues exhale carbon dioxide in 

 darkness and that non-chlorophyllous parts do the same even when illuminated. 

 De Saussure proved that both water and carbon dioxide are produced during 

 respiration, and was probably aware that respiration continued in green parts 

 exposed to light, although he did not definitely establish the simultaneity of 

 respiration or 'inspiration' and photosynthetic assimilation or 'expiration.' It had 

 probably long been known that the exhalation of carbon dioxide was due to a vital 

 process analogous to that occurring in animals, when Liebig disproved the view that 

 it was absorbed as such from the ground and was not a metabolic product 2 . Meyen 

 was probably the first to clearly show that the respiration and assimilation of carbon 

 dioxide are two distinct and independent processes, and he also correctly enunciated 

 their respective values to the plant. Similarly Dutrochet, and especially Garreau 

 and Mohl, held correct views with regard to the relationship between respiration 

 and photosynthetic assimilation. Both processes were, however, unfortunately 

 termed respiration, which was supposed to differ in the daytime from what it was 

 at night, until Sachs in 1865 pointed out that only the processes concerned in the 

 production of carbon dioxide can be rightly termed respiration or breathing 8 . 



SECTION 96. The Products of Aerobic Respiration. 



Even in adult organs the excretion of respiratory and other metabolic 

 products is difficult or impossible, except in the cases of carbon dioxide and 

 water. It seems probable that even the last act of physiological combustion 

 may differ somewhat in different plants, the substances produced and con- 

 sumed not being always precisely the same : thus not only carbon dioxide 

 and water but also organic acids may be derived from the combustion of the 

 organic carbon-compounds to which most plants are restricted, and some- 

 times large quantities of organic acids may appear. Moreover in certain 

 bacteria energy is obtained not from the combustion of carbon-compounds 

 but by the oxidation of sulphuretted hydrogen to sulphur and sulphuric 

 acid (sulphur-bacteria), ammonia to nitrous and nitric acid (nitro-bacteria), 

 and even ferrous into ferric oxide (iron-bacteria) 4 . Beggiatoa is actually 

 able to oxidize from two to four times its own weight of sulphur in one to 



1 Malpighi, Opera omnia, 1867, I, p. 108; Scheele, Chem. Abb. von d. Luft, libers, v. Berg- 

 mann, 1777, p. ia; Ingenhousz, Versuche mit Pflanzen, 1786; Saussnre, Rech. chim., 1804, and 

 later works previously quoted. 



* Liebig, Die org. Chemie in ihrer Anwendung auf Agric. u. Physiol., 1840, p. 30. 



3 Meyen, Pflanzenphysiol., 1838, Bd. II, p. 162 ; Dutrochet, Memoires, Bruxelles, 1837, pp. 169, 

 185; Garreau, Ann. d. sci. nat., 1851, iii. ser., T. XVI, p. 290; Mohl, Grundziige d. Anat. u. 

 Physiol., 1851, p. 86. 



* \\inogradsky, Bot. Zeitung, 1888, p. 261 ; Molisch, Die Pflanze in ihren Beziehungen z. Eisen, 

 1892, p. 60. Cf. Sects. 23, 63; also Pfeffer, Energetik, 1892, p. 208. 



