402 



MK. J. It. LAWES, DH. GILBERT, Wl> DB. PUGH OB 



Experiments. Series 8. 



In order to bring oul more clearly the influence of anRghl before the exhaustion, a 

 scries of experiments were made, in which two containing the duplicate quan- 



tities of plant, wen; cadi kepi covered with paper for some rime, and then, from tw< 

 to thirty minutes before commencing the exhaustion, the paper was removed from one of 

 them, both being then exhausted, — the process continuing ten, fifteen, or twenty minute-. 

 The following results were obtained. 



Table VI. — Showing the amount and composition of the Gas evolved into a Torricellian 

 vacuum, by duplicate quantities of plant, both kept in the dark for some time, and 

 then one exposed to sunlight for about twenty minutes, when both were submitted 

 to exhaustion. 



The comparison of the results in this Table with those in Table V., shows that the 

 oxygen must have been liberated from the carbon, and been retained within the cells, 

 until the instant of the exhaustion, as the gas was evolved from all parts of the leaf, 

 and not from the surrounding water, as soon as the pressure was removed. 



The conclusions to be drawn from the above several Series of experiments are not 

 without an interesting bearing upon our present subject. 



1. Carbonic acid, within growing vegetable cells, and intercellular passages, which 

 are penetrated by the sun's rays, suffers decomposition with the evolution of oxygen. 

 the latter remaining in the plant or being evolved from it. This takes place very 

 rapidly after the penetration of the sun's rays. 



