ASSIMILATION OF AZOTE. 43 



in ploughing down this second crop we restore such a quantity of 

 organic or organizable matter, that, all things taken into account, 

 the ground actually receives more from the atmosphere than was 

 taken away from it in the first cutting. 



The latest experiments of physiologists would seem to show that 

 plants merely take carbon from the air, and appropriate the elements 

 of water. But the ideas which are now generally adopted in regard to 

 the active principle of manures make it difficult to conceive that the 

 soil, by receiving non-azotized matters only, could acquire the degree 

 of fertility which is certainly obtained from the cultivation of those 

 crops that are called ameliorating^ a fertility which enables us to 

 folk)\v these crops with others, rich in azotized principles. 



There is therefore reason for believing that the ploughing in of 

 certain green crops, and fallowing, are not effectual merely by in- 

 troducing carbon, hydrogen, and oxygen, but azote also into the 

 soil. And it is absolutely necessary that this should be so, in order 

 that the fertility of those lands may be maintained which, from theij. 

 position, can receive no manures from without. Let us take, for 

 example, a farm laid out for the growth of white crops, and the 

 rearing of cattle. Every year there is an exportation of grain, of 

 flesh, and of the produce of the dairy ; that is to say, there is inces- 

 sant exportation without any perceptible importation of azotized 

 matter. Nevertheless, the soil maintains its fertility ; its losses are 

 repaired by the principles which, in a good system of cultivation, 

 pass from the atmosphere into the earth ; and among the number of 

 these fertilizing principles it is beyond all question that azote must 

 be present, in order that so much of this element as has been ex- 

 ported may be replaced. 



The best established facts in agriculture, therefore, concurred in 

 showing that azote is among the number of the elements that are 

 fixed by plants during their growth. Still, as this truth had not been 

 proved by the experiments of physiologists, the question had to be 

 considered as yet undecided. It was with the hope of clearing up 

 every thing in connection with it that I undertook the series of ex- 

 periments, the chief features of which I shall now detail.* 



I had necessarily to follow a method of inquiry different from any 

 which had yet been taken ; I had no chance of arriving at more de- 

 finite results than those which had been already come to, had I cho- 

 sen the old line of investigation. I therefore called in the aid of 

 elementary analysis, with a view of comparing the composition of 

 the seed with the composition of the harvest produced from it, at the 

 sole cost of water and the air. By proceeding in this way I believed 

 that the problem was capable of solution : without flattering my- 

 self that I have completely resolved it, I conceive that something 

 has been done in the right direction. The subject is one of the most 

 delicate imaginable, and lie who enters it requires indulgence. 



For soil, I made use of burned clay or silicious sand freed from 

 all organic matter by proper calcination. In this soil, moistened 



♦ Boussb^Ut, Annates de chimie et de physique, t. Lxvii. p. 5, 2"* s6rie, &an6e 1838 



