168 EFFECT OF LIGHT UPON PLANTS. 



pomane Mancinella^ or, as it is commonly believed, under 

 a Walnut-tree, are probably to be attributed as much to 

 poisonous secretions as to the air those plants evolve. 



Dr. Ingenhousz introduced leaves into glass jars filled 

 with water, which he inverted in a tub of the same water, 

 and placed the whole together in the sun-shine. From 

 their under sides came streams or bubbles of air, which 

 collected in the inverted bottom of each jar. The air 

 thus procured proved oxygen gas, more or less pure. 

 The Nymph(sa alba, Engl. Bot. t. 160, affords an ex- 

 traordinary abundance of it. Dr. Ingenhousz observed 

 plants to be very various in their mode of emitting these 

 bubbles, but it was always uniform in the same species. 

 Air collected from water placed in similar circumstances 

 without plants, proved not oxygen, but much worse 

 than common air, viz. carbonic acid gas, which follow- 

 ing chemists have confirmed, and which we have already 

 mentioned. Ingenhousz also found the air collected 

 from plants under water in the dark worse than common 

 air, especially that from walnut-leaves ; which confirms 

 the common opinion, above alluded to, respecting this 



tree. 



Plants purify air very quickly. A vine-leaf in an 

 ounce phial of carbonic acid gas, that immediately extin- 

 guished a candle, placed in the sun, without water, 

 changed it to pure respirable air in an hour and half. 

 Dr. Priestley found plants to alter even unmixed inflam- 

 mable air, or hydrogefi, especially the Epilobium hirsu- 

 tum, if I mistake not, and Polygonum Hydropiper. 



Succulent plants are found to afford most air, in con- 

 sequence of the abundance of their Cellular Integument, 



