428 Dr. Gardner's Researches on the Functions of Plants. 



unphilosophical view, for it leaves out of consideration the ca- 

 pacity of the sap to absorb them and its condition as to gaseous 

 saturation. In making experiments on the subject, it is also 

 necessary to consider the functions of the plant. 



12. On the 25th of June 1844, I commenced a series of 

 observations to determine the action of uninjured roots of 

 Datura and blue grass on the gas dissolved in pump-water, 

 which accurately represents the soil-fluid. The plants were 

 obtained as detailed in section 7; they were placed in vessels 

 resembling a bird-fountain, which were capable of being re- 

 plenished with water to compensate for the evaporation of the 

 leaves, and also of collecting any gas passing from the roots. 

 Three sets of experiments were made : A, the roots and leaves 

 were placed in darkness ; B, both portions were exposed to 

 bright diffused light; C, the leaves were illuminated, but the 

 roots in darkness. 



13. On the evening of the 25th of June, two sets of plants 

 were arranged according to these plans. The Daturas, B, 

 yielded the next morning at 11, a gas the composition of 

 which was N 96*6, O 3*4 percent.; these two plants were 

 then placed in a dark cupboard for thirty-six hours and evolved 

 no gas whatever; on again exposing them to light, they pro- 

 duced a mixture of N 96*2, O 3*8 per cent, as the mean of six 

 analyses. The grass plants, B, gave off but little gas, and 

 only enough was collected for two measures, which yielded a 

 mean of N 96, O 4 per cent. 



The plants C conducted themselves in the same way as B ; 

 the Daturas gave gas for six analyses, the mean of which was 

 N 96-5, O 3*5 per cent. 



The plants A, placed in darkness, gave no gas whatever, 

 although they were attended to for five days. 



14. We conclude that roots appear to evolve gas unequally 

 in quantity; that the action of light on the leaves is essential 

 to this phenomenon ; and thirdly, it, the exposure of the root, 

 does not seem to have any effect on the result. I do not be- 

 lieve 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 water, so that all the carbonic acid is withdrawn and most of 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 dis- 

 turbance was not a mechanical effect of light and heat, I sa- 

 tisfied myself by observations at the time ; and the results of 

 Prof. Morren (Ann. de Chimie, Src, 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 ob- 

 served. 



