CH. I.] SOWING. 35 



spring water, for it then contains carburetted hydrogen 

 and other matters noxious to vegetables. These last 

 named waters, if obHged to be employed to tender 

 plants, should have a pint of the ammoniacal ivater 

 of the gas-works, mixed thoroughly with every sLxty 

 gallons, an hour or two before they are used. 



The presence of .one of the constituent gases of the 

 atmosphere, oxygen, is also essential to germination. 

 Ray proved that lettuce seeds would not germinate in 

 the exhausted receiver of an air pump, though they 

 did so when the air was re-admitted ^ ; and though 

 the experiments of Homberg throw some doubt upon 

 this conclusion b, yet it was fully confirmed by the re- 

 searches of Boyle, Muschenbroek, Boerhaave and 

 Saussure, for they showed that Homberg must have 

 employed an imperfect apparatus, and their expe- 

 riments embraced many other seeds than those of 

 the lettuce. So soon as pneumatic chemistry de- 

 monstrated that the atmospheric air is composed of 

 several gases, \iz. : 



Oxygen 21 



Nitrogen 79 



100 

 with about one per cent, of aqueous vapour in the 

 driest weather, and about one part in every thousand 

 of carbonic acid gas, the question then arose which 



^ Phil. Trans. No. xiii. »> Mem. French Acad, for 1693. 



D 2 



