430 History of the English Landed Interest. 



been found to be in entire accord over the phenomena of the 

 vegetable economy, and where experts were at variance, it was 

 impossible for amateurs to decide. For instance, authorities 

 differed as to the mutual effects of vegetables and the 

 atmosphere upon one another. Davy followed Priestley and 

 Ingenhous in attributing to plants a purifying effect on the 

 air. Ellis and others, though admitting that many vegetables 

 absorbed carbonic acid and furnished oxygen, believed that such 

 an operation was partial and accidental. That an atmosphere 

 overcharged with carbonic acid was purified by the agency of 

 plants all chemists were ready to admit, but they had not yet 

 learned that chlorophyll has the inherent gift, in the presence 

 of sunlight, of releasing the oxygen and absorbing the carbon 

 of the carbonic acid gas, while away from the sun the process 

 is reversed. In the same way their knowledge of the action 

 of water on plant life was imperfect. Braconnot maintained 

 that many of the agents of the vegetable economy, like those 

 of the animal economy, acted only as stimulants. Pure water, 

 according to them, afforded the one necessary nutriment, and 

 what plants absorbed from manures and other ingredients of 

 the soil did not become part and parcel of their substance. 



Davy collated a mass of evidence tending towards a con- 

 trary conclusion. Bringing his advanced electrical learning 

 to bear on the subject, he made even the purest of waters ^ 

 yield up its alkalies and other earths under the spell of the 

 voltaic battery, and ascribed to their presence the supposed 

 fertilising effects of the liquid. He next attempted to grow 

 oats out of unadulterated carbonate of lime,^ kept constantly 

 moist, but not saturated, with distilled water. Failing, he 

 burned the withered plant, analysed its ash, and discovered a 

 preponderance of carbonate of lime and a deficiency of siliceous 

 matters. Recalling to mind the experiences of Jacquin with 

 marine plants propagated in soils uninfluenced by the sea, the 



^ Sir Humphry Davy stated that even " distilled water was far from 

 being free from saline impregnations." Vide, Quarterly Review, vol. xi. 

 1814, sub voc. " Davy's Agri. Chem." 



2 I use the term carbonate of lime in preference to the correct one, car- 

 bonate of calcium, as being synchronous with the times under discussion. 



