DISCOVERY OF THE SOURCE OF PLANTS' CARBON. 11 



of crops was unnecessary, provided that a thorough 

 system of tillage was carried out. Manures also, ac- 

 cording to him, might be entirely dispensed with 

 under his system of cultivation, for the true function 

 of all manures is to aid in the pulverisation of the 

 soil by fermentation. 



The first really valuable scientific facts contributed 

 to the science were made by Priestley, Bonnet, Ingen- 

 housz, and Senebier. 



Discovery of the Source of Plants Carbon. 



To Charles Bonnet (1720-1793), a Swiss naturalist, 

 is due the credit of having made the first contribu- 

 tion to a discovery of very great importance viz., 

 the true source of the carbon, which we now know 

 forms so large a portion of the plant - substance. 

 Bonnet, who had devoted himself to the question of 

 the function of leaves, noticed that when these were 

 immersed in water bubbles were seen, after a time, 

 to collect on their surface. De la Hire, it ought 

 to be pointed out, had noticed this same fact about 

 sixty years earlier. It was left to Priestley, how- 

 ever, to identify these bubbles with the gas he had 

 a short time previously discovered viz., oxygen. 

 Priestley had observed, about this time, the interest- 

 ing fact that plants possessed the power of purify- 

 ing air vitiated by the presence of animal life. 1 The 



1 Priestley, however, did riot realise that carbonic acid gas was a 

 necessary plant-food ; on the contrary, he considered it to have a 



