60 



INVESTIGATION INTO THE AMOUNT OF WATEB 



It may be supposed, indeed, that here we have evidence of a 

 superior power in the leguminous as compared with the grami- 

 naceous plants, of obtaining their nitrogen from the atmosphere 

 rather than from the soil. However this may be, many experi- 

 ments of our own have convinced us that, especially in the growth 

 of the graminaceous grains, there is never an increased acreage 

 yield of nitrogen in any degree approaching that supplied by 

 manure, and, independently of results of a more direct and 

 practical kind, it has been observed by several experimenters, 

 that during the growth of plants there is a constant evolution of 

 nitrogen from their leaves. 



Thus De Saussure, in his ' Recherches Chimiques sur la Vege- 

 tation,' pp. 40-43, gives the results of experiments on this subject, 

 and he comes to the conclusion that the amount of nitrogen given 

 off bears a direct relation to that of oxygen assimilated by the 

 plant from the absorbed carbonic acid. His experiments more- 

 over were made with the Vetch, which, as will be remembered, 

 is a member of the Leguminous family of plants, in which, as 

 compared with the Graminaceous family, we would suppose the 

 evolution of nitrogen to be less considerable. 



Daubeny, again, in his 1 Memoir on the Action of Light upon 

 Plants, and of Plants upon the Atmosphere,' in the Philosophical 

 Transactions for 1836, Part I., arrives at a somewhat similar 

 result ; whilst more recently Draper, in his * Chemistry of Plants,' 

 pp. 184, 185, and context, ascertained in several experiments the 

 amount of nitrogen given off during the growth of plants, and 

 seeks to establish the following conclusions: that "when the 

 leaves of plants under the influence of light decompose carbonic 

 acid, they assimilate all the carbon, and a certain proportion of 

 oxygen disappears ; at the same time they emit a volume of 

 nitrogen equal to that of the oxygen consumed* This disap- 

 pearance of oxygen and appearance of nitrogen are thus con- 

 nected with each other: they are equivalent phenomena. The 

 emission of nitrogen is thus shown not to be a mere accidental 

 result, but to be profoundly connected with the whole physio- 

 logical action At this stage of the inquiry a remarkable 



analogy appears between the function of digestion in animals and 

 the same functions in plants. Liebig has shown how, from the 

 transformation of the stomach itself, food becomes acted upon, 

 and is turned into chyme ; an obscure species of fermentation, 

 brought about by the action of nitrogenized bodies. So in like 

 manner, in plants, the decay of a nitrogenized body is intimately 

 connected with the assimilation of carbon ; for, as I have stated, 

 the process here under discussion is a true digestive and not a 



* The italics are those of the author. 



