FUNCTION.] ROOTS GIVE OFF CARBONIC ACID. 185 



although they were attended to for five days. We con- 

 cluded that roots appear to evolve gas unequally in quantity ; 

 that the action of light on the leaves is essential to this phe- 

 nomenon ; and thirdly, the exposure of the root, does not 

 seem to have any effect on the result. I do not believe that 

 the gas is evolved from the interior of the plant, but that the 

 roots disturb the equilibrium of the mixture in the water, so 

 that all the carbonic acid is withdrawn, and most of the 

 oxygen, leaving behind the sparingly soluble nitrogen, which 

 acquires the elastic condition." That this gaseous disturbance 

 was not a mechanical effect of light and heat, he satisfied 

 himself by observations at the time ; " and the results of 

 Professor Morren (Ann. de Chimie, fyc., Sept. 1844) show 

 that the sun's light liberates carbonic acid and nitrogen, 

 accumulating oxygen in the water, which is opposed to the 

 effects here observed." 



" The gas of the pump-water was N 48, O 22, CO 2 30 

 per cent., therefore the roots absorbed carbonic acid and 

 oxygen in the same way as a porous system containing the 

 normal plant atmosphere, N 86*75, O 13*25 per cent.; this 

 continued during daylight, or during the activity of the 

 vegetable, but in darkness all the gas of the water is taken 

 up without any selection." (Phil. Mag. xxviii. 427.) 



There seems, however, to be no doubt that the roots of 

 plants do give off carbonic acid. The discovery of this is 

 claimed by Dr. John Murray, who, in a letter addressed to 

 the Editor of the Gardeners' Chronicle, asserts that in 

 1818 he proved the fact experimentally by growing the bulbs 

 of Hyacinths, &c. in distilled water. He adds, " I am 

 possessed of a very remarkable specimen proving that the 

 carbonic acid gas secreted by the roots of the Lichen does 

 decompose the silicated alkali of glass. It is a piece of old 

 glass from a window at St. Cross, near Winchester. When 

 put into my hands, it was beautifully mantled with a brilliant 

 Lichen ; which being removed, discovered the surface of the 

 glass beneath, corroded and completely grooved or wormed." 

 This has been also ascertained by Messrs. Wiegmann and 

 Polsdorff. It appears from their researches, as reported in 

 the Annals of Chemistry, that the roots of living plants 



