SECT. II. GASES. 53 



Beans, Peas, and Cresses, by placing them in horse- 

 hair, or in pure sand, and moistening them with 

 distilled water. They grew indeed, and some of 

 them even flowered, but never produced perfect 

 seeds.* And Giobert and Hassenfratz, who had 

 made similar experiments, had also similar results. 

 It is plain therefore that some essential principle 

 of nourishment was wanting, which is furnished 

 by the soil ; and that atmospheric air and water 

 are not the only principles constituting the food of 

 plants. 



But as in germination so also in the progress of Or at least 

 vegetation, it is part only of the component prin- compo- U ' 

 ciple of the atmospheric air that are adapted to the nent P arU - 

 purposes of vegetable nutrition, and selected by 

 the plant as a food. Let us take them in the order 

 of their reversed proportions. 



SUBSECTION I. 



Carbonic acid gas. In the process of the ger- 

 mination of the seed, the effect of the application 

 of carbonic acid gas was found to be altogether 

 prejudicial. But in the process of subsequent ve- Beneficial 

 getation its application has been found, on the con- t [ 

 trary, to be extremely beneficial. Plants will not lun 

 indeed vegetate in an atmosphere of pure carbonic 

 acid, as was first ascertained by Dr. Priestley, who 

 found that sprigs of mint growing in water, and 

 * Sur la Veg, chap, viii. sect, i. 



