GIVEN OFF BY PLANTS DURING THEIR GROWTH. 



61 



respiratory process. And as there are facts which seem to show 

 that the primary action of the light is not upon the carbonic acid, 

 but upon the nitrogenized ferment, the decomposition of the gas 

 ensuing as a secondary result, is it not probable that Chloro- 

 phyl is the body which in vegetables answers to the Chyle of 

 animals? The oxygen which disappears during the decom- 

 position of carbonic acid, disappears to bring about the erema- 

 causis of the nitrogenized body. And have not the gum, the 

 starch, the lignin, and other carbonaceous constituents of plants, 

 all originally existed in and passed through the green stage ?" 



Mulder, again, from purely chemical considerations, and, like 

 the observers alluded to above, altogether independently of the 

 important practical application of the phenomena to which we 

 wish to direct attention, admits the constant evolution of nitrogen 

 during the growth of plants, and that the source of this nitrogen 

 must obviously be the compounds containing it already existing 

 in the plants ; but he maintains with more or less apparent reason 

 that the relation of nitrogen given off to that of oxygen assimi- 

 lated from the absorbed carbonic acid must depend materially 

 upon the composition of the compounds to be formed. Thus, 

 referring to Draper's experiments, he says (see his Chemistry of 

 Vegetable and Animal Physiology, Part IV., p. 778), "But 

 this simplicity of relation is in my opinion accidental. The car- 

 bonic acid is employed for the production of various organic 

 bodies, which cannot possibly be the same in all plants. Conse- 

 quently, the quantity of oxygen given off cannot be a constant 

 one. This variety of product also renders it impossible that a 

 constant amount of nitrogenous substance should be required for 

 the decomposition of the carbonic acid.*' 



It may be taken then as a well-ascertained fact, that the evolu- 

 tion of nitrogen is a constant and coincident attendant on the 

 growth and accumulation of a plant ; whilst it would seem that 

 both the results of practice and the reasonings of the chemist 

 would lead us to suppose that this loss is greater in some cases 

 than in others. 



Let it once be admitted in agricultural science that there is 

 a definite expenditure or consumption of the nitrogenous bodies 

 derived through the roots connected with the fixation and ela- 

 boration of certain constituents of plants, and that this is greater 

 or less according to the sources or the exact composition or 

 state of elaboration of the products, and an important step will 

 be gained towards a clearer conception of the principles involved 

 in the alternation, in a course of cropping of plants, of varying 

 products and habits of growth. In one of our papers On Agri- 

 cultural Chemistry in the Journal of the Royal Agricultural 

 Society (Part L, 1847), we have ventured an opinion as to the 



