of the Organic Systems of Vegetables. 99 



solid contents ; for Saussure has proved, which other experi- 

 ments have verified, that seeds, bulbs, slips, &c., made to grow 

 under such circumstances, when incinerated, and the unassimi- 

 lated water driven off, weigh less than similar plants did before 

 their exclusion from the light; so that matter has been lost by 

 them in the formation of carbonic acid, and none gained by 

 assimilation of their food. In germinating seeds the same 

 phenomena notoriously occur. 



Again, I have found by other experiments, that if vigorously 

 growing plants be inclosed in bottles containing a little lime 

 water, and the oxygen be converted into carbonic acid by the 

 combustion of a taper and then precipitated, that if kept in 

 the sunlight for a few hours, a small quantity of oxygen is 

 reproduced, which appears to be derived from the decompo- 

 sition of the water ; as it can scarcely be supposed that the 

 chalk affords it : and this opinion receives further confirmation 

 from an experiment of Sir Humphry Davy ; in which a vine- 

 leaf was inclosed in a vessel in which aqueous vapour was con- 

 veyed through mercury from water that had been a long while 

 in a state of ebullition, and yet a little oxygen was liberated, 

 which Sir Humphry Davy believed to be derived from the 

 decomposition of the water which decomposition is a vital 

 action of the plant assisted by the stimulus of light. Further- 

 more, experiments shew that whenever carbonic acid is pro- 

 duced in excess, the solid substance of the plant is lessened ; 

 but on the contrary, when oxygen is evolved, that its solid 

 materials are increased. 



From these, which have been selected from numerous other 

 experiments, are we not justified in concluding that the pro- 

 duction of oxygen and its converse, the formation of carbonic 

 acid, are the unvarying results of two different functions : viz., 

 this of respiration, that of digestion ; and that both are vege- 

 tative actions, dependant on vitality ? 



To conclude, the formation of carbonic acid is constant both 

 by day and by night, during the life of the vegetable ; it is 

 equally carried on whether in sickness, or in health ; it is 

 essential to its existence for the sustentation of its irritability ; 

 for, if deprived of oxygen and confined in carbonic acid gas, 

 plants, like animals, quickly die. This function, which is per- 



H2 



