C 196 ] 



eral efficacy. It may, however, be safely adopted, for 

 if it should fail in destroying the fly, it will at least be* 

 an useful manure to the land. 



After the roots and leaves of the infant plant are 

 formed, the cells and tubes throughout its structure 

 become filled with fluid, which is usually supplied from 

 the soil, and the function of nourishment is perform- 

 ed by the action of its organs upon the external ele- 

 ments. The constituent parts of the air are subser- 

 vient to this process ; but, as it might be expected, 

 they act differently under different circumstances. 



When a growing plant, the roots of which are sup- 

 plied with proper nourishment, is exposed in the pre- 

 sence of solar light to a given quantity of atmospheri- 

 cal air, containing its due proportion of carbonic acid, 

 the carbonic acid after a certain time is destroyed, and 

 a certain quantity of oxygene is found in its place. If 

 new quantities of carbonic acid gas be supplied, the 

 same result occurs ; so that carbon is added to plants 

 from the air by the process of vegetation in sunshine j 

 and oxygene is added to the atmosphere. 



This circumstance is proved by a number of ex- 

 periments made by Drs. Priestley, Ingenhousz and 

 Woodhouse, and M. T. de Saussure ; many of which 

 I have repeated with similar results. - The absorption 

 of carbonic acid gas, and the production of oxygene 

 are performed by the leaf; and leaves recently separ- 

 ated from the tree effect the change, when confined in 

 portions of air containing carbonic acid ; and absorb 

 carbonic acid and produce oxygene, even when im- 

 mersed in water holding carbonic acid in solution. 



