VEGETABLE PHYSIOLOGY. 35 



hypothesis is unworthy of detailed notice. His subsequent 

 opinions respecting the operation of carbon, do not seem to be 

 better founded. This philosopher, as well as Berthollet, deter- 

 mined many important facts. There is a very evident connexion 

 between the decomposition of carbonic acid gas and the green color 

 of leaves, as is shown by the following results. Green leaves onlv 

 yield oxygen gas ; the parenchymatous substance of the leaf is 

 the seat of decomposition of the gas, and of the green color ; 

 the coloration will take place in leaves separated from the stem, 

 so that there can be no living action in them ; consequently the 

 coloration is independent of the life of the plant. 



It appears from the various experiments of Berthollet, Senebier 

 and others, that solutions of the colorable parts of leaves are 

 rendered red or green according to the predominance of acid or 

 alkaline matter ; but similar effects will be also induced on entire 

 leaves. Etiolated leaves, and those reddened by age, pass into 

 green in alkaline fluids ; those that are yellow from decomposition, 

 become brown in the same circumstances. Ellis observed, that 

 if the green color had been previously affected by the action of 

 water, that alkalies did not restore it. On these facts this physi- 

 ologist ventures to presume, " that these same agents (acids and 

 alkalies) if present, will exert a similar action on leaves-during 

 their growth." 



He first establishes the existence of a large quantity of alkaline 

 matter in the leaves, and shows that the separation of the carbonic 

 acid, and its subsequent decomposition, render the alkali pre- 

 dominant, and consequently better fitted to exert its specific 

 influence " on the colorable juices of the plant," which produces 

 the color of the leaf. So that according to Mr. Ellis's views, 

 the decomposition of the carbonic acid answers two purposes, 

 the production of oxygen gas and the formation of the green 

 color. 



If the green color depend on the predominancy of alkali, it 

 may be reasonably supposed that the white color depends on a 

 deficiency of it. Senebier's experiments support this supposition, 

 and his results have been confirmed by Davy and others. This 

 whiteness of color will continue so long as the acid abounds ; 



