18.2 CHEMICAL AGENCY 



long a question whether the decomposition of carbonic 

 acid by plants was due to the luminous or the chemical 

 rays. It is now clearly established that the luminous 

 rays are the most active in producing this effect ; which 

 they do indirectly, by exciting the vital powers of the 

 organized structures. Therefore we would refer this 

 phenomenon of gaseous decomposition to a vital power 

 quickened by luminous excitement.* 



* The following memoirs and works are necessary to a complete 

 history of the inquiry : Experiments and observations relating to 

 various branches of natural philosophy, with a continuation of the 

 observation on air: by Dr. Priestley. London, ]779. Aiemoires 

 Phi/sico-chimiques, Sfc. : by J. Senebier. Experiences sur les vege- 

 taux, by Dela Ville : Paris, 1782 ; and Phil. Trans. 17.82. Obser- 

 vations sur les experiences de M. Ingenhousz : by De la Ville ; lioz. 

 obs. 23, 290. Experiences propres a dttvelopper les ejfets de la 

 lumiere sur certaines plantes: by Tessier; Mem. de 1'Ac. des Sc 

 de Paris, 1783, p. 132; Licht. Mag. iv. 4, 140. Sur la vertu de 

 Icaa impregnee a" air fixe pour en obtenir, par le moyen des plantes et 

 de la lumiere du soleil, de lair dephlogistique : by Ingenhousz ; 

 Koz. obs. 24, 337. Experiences sur V action de la lumiere solaire 

 dans la vegetation: by Senebier; Geneve et Paris, 1788, p. 61. 

 Extrait des experiences de M. Senebier sur Faction de la lumiere 

 sol'dre dans la vegetation: by Hasenfratz; Ann. Chim. iii. 2nd. 

 ser. 266. Experiences relatives a I influence de la Jumiere sur 

 quelques vegetaux: by De Candolle ; Jour, de Ph. Iii. 124: Voigt's 

 Mag. ii. 483 ; Gilb. Ann. xiii. 372 ; Mem. des Sav. Etr. i. 329. 

 Reckerches chimiques sur la vegetation : by Saussure ; Ann. Chim. 

 1. 225 ; Jour, de Ph. Ivii. p. 393 ; Gilb. Ann. xviii 208. Recherches 

 sur la respiration des plantes ex Donees a la lumiere da soleil', by 

 Ruhland; Ann. Ch. Ph. iii. .411 ; Jour, de Ph. 1816. On the 

 action of light upon plants, and of plants upon the atmosphere : by 

 Dr. Daubeny; Phil. Trans, cxxvii January, 1838. On the action 

 of yellow light in producing the green colour, and of indigo light on 

 the movements of plants: by P. Gardner; Phil. Mag. xxiv. ; Bibl. 

 Univ. xlix. p. 376, and Iii. p. 381. On, the influence of light on 

 plmts: by R. Hunt; Phil. Mag. xxiv. p. 90; Bibl. Univ. xlix. 

 p. 383; Atlien. 1844 Note on the decomposition of carbonic acid 

 by the leaves of plants, under the influence of yellow light : by 

 Draper; Phil. Mag. xxv. p. 169. On the action of the yellow rays 

 of light on vegetation: by Harkness ; Phil. Mag. xxv. p. 339. 

 Influence des radons solaires sur la vegetation: by Zantedeschi ; 

 Inst. No. 541, p. 157. 



