AEROBIC RESPIRATION 521 



In parts containing but little chlorophyll respiration may always be more active 

 than photosynthctic assimilation, but even the slight amount of chlorophyll present 

 in Neottia nidus-avis suffices to cause a feeble evolution of oxygen in bright light '. 

 Similarly many fruits evolve less carbon dioxide during the daytime, until as they 

 ripen the chlorophyll is gradually decomposed and the power of photosynthesis 

 lost 2 . Similarly respiration is at first more active than photosynthetic assimilation 

 in buds, seedlings, &c., although the latter soon surpasses the former and increases 

 until the plant becomes adult 3 . As the temperature rises the respiratory activity 

 continually increases, whereas beyond a certain optimum the activity with which 

 carbon dioxide can be assimilated decreases. Hence at a certain point the curves 

 cross, and even in strong light more oxygen is consumed by respiration than is 

 produced by the assimilation of carbon dioxide. 



Respiration is markedly influenced by changes of temperature, but 

 under similar conditions it is most active in the more vigorous parts and 

 organs : thus resting tubers, bulbs, buds, &c. exhibit a feebler respiratory 

 activity than growing shoots, in which again respiration is more active than 

 in adult leaves and branches. No definite and constant relationship exists 

 between growth and respiratory activity, for a variety of other factors 

 influence the former. Indeed many adult organs respire energetically, 

 while in the spadix of aroids respiration and the production of heat attain 

 a simultaneous maximum which does not coincide with the period of most 

 active growth. Moreover beyond a certain optimal temperature growth 

 is retarded, whereas respiration increases until death ensues. 



Active embryonic cells are usually rich in protoplasm, and hence it 

 is often the case, as Garreau observed, that a certain correspondence exists 

 between richness in proteid and respiratory activity. The energy of respira- 

 tion is, however, not directly dependent, as Palladin supposes, upon the 

 quantity of proteids present 4 , for in spite of the abundance of the latter 



1 Drude, Biol. v. Monotropa u. Neottia, 1873, p. 18. On other Phanerogams containing but 

 little or no chlorophyll, cf. Lory, Ann. d. sci. nat, 1847, iii. se'r., T. vin, p. 160; Bonnier et 

 Mangin, ibid., 1884, v '- ser., T. xvm, p. 332 ; also Sect. 64. 



' 2 Ingenhousz, Versuche mit Pflanzen, 1786, Bd. I, p. 72 ; Bd. n, p. 223; deSaussure, Rech. chim., 

 1804, pp. 57, 129; Ann. d. chim. et d. phys., 1821, T. xix, p. 158; Berard, ibid., 1821, T. LXXVI, 

 pp. 152, 225; Fre'my, Compt. rend., 1864, T. LVIII, p. 656; Cahonrs, ibid., pp. 495, 653. Cf. 

 Sect. 109. A weak evolution of oxygen may actually be detected, by means of the bacterium method, 

 from the chlorophyllous cells of certain young green fruits when exposed to light (Ewart, Journ. of 

 Linn. Soc., 1896, Vol. xxxi, p. 437). 



3 Ingenhousz, I.e., Bd. I, pp. 112, 355; Garreau, Ann. d. sci. nat., 1851, iii. ser., T. xvi, 

 p. 272; Corenwinder, Ann. d. chim. et d. phys., 1858, iii. se'r., T. LIV, p. 326, and 1878, v. ser., 

 T. xiv, p. 118; Ann. d. sci. nat., 1864, v. se'r., T. I, pp 297, &c. For the stage of development 

 at which a power of evolving oxygen is attained by the leaves of the commoner trees, &c., see Ewart, 

 Journ. of Linn. Soc., 1896, Vol. xxxi, p. 452. 



4 Garreau, Ann. d. sci. nat., 1851, iii. se'r., T. xv, p. 36 ; T. xvi, p. 292 ; Palladin, Rev. gen. d. 

 Bot., 1893, T. v, p. 472. 



