SECT. II. GASES. 63 



its pure state, is not only incapable of affording a 

 vegetable aliment, but is not even inhaled into the 

 plant. But nitrogene is found in almost all vege- 

 tables, particularly in the wood, in extract, and in 

 their green parts. Whence then is their nitrogene 

 derived ? From the extractive principle of vegetable 

 mould. 



SUBSECTION IV. 



Hydrogene Gas. A plant of the Epilobium 

 hirsutum^ which was confined by Priestley in a 

 receiver filled with inflammable air or hydrogene, 

 consumed one-third of its atmosphere and was still 

 green.* Hence Priestley inferred that it serves as Thought 

 a vegetable food, and constitutes even the true and i e y toTe'a 

 proper pabulum of the plant. But the experiments 

 of later phytologists do not at all countenance this 

 opinion. Saussure introduced a plant of the Ly- 

 thrum Salicaria into a receiver containing sixty 

 cubic inches of hydrogene gas, and exposed it to 

 the sun. Its vegetation was perhaps somewhat 

 more vigorous than that of plants confined in an 

 atmosphere of nitrogene ; but it had abstracted 

 no nourishment from its atmosphere, nor effected 

 any material change upon it. For at the end of 

 five weeks of experiment, when its asmosphere was 

 fired by the electric spark along with the proper 

 quantity of oxygene, the result was the formation 



* Priestley on Air, vol. iv. p, 323. 

 5 



