ASSIMILATION OF ELEMENTS. 49 



Second. That wheat and oats grown in the same circumstances, 

 took carbon, hydrogen, and oxygen from the air and water around 

 them ; but that analysis showed no increase of azote in these plants 

 after their maturity. 



The mode of experimenting followed had it in view simply to 

 determine the assimilation of azote by certain vegetables, without 

 entering into the question of the means by which this was effected ; 

 and, indeed, in reference to the point, I can only offer conjectures. 



Azote may enter the living frame of plants directly, or, as M. 

 Piobert has maintained, in the state of solution in the water, always 

 aerated, which is taken up by their roots.* The observations of 

 vegetable physiologists are not generaly favorable to this view. It 

 is farther possible that the element in question may be derived from 

 ammoniacal vapors, which, according to some philosophers, exist in 

 infinitely small proportion in our atmosphere. These vapors, dis- 

 solved by rains and dews, would readily make their way into plants, 

 and might there undergo elaboration. 



It is long since Saussure alluded to the probable influence of am- 

 moniacal vapors upon vegetation. Prof. Liebig has more recently 

 maintained the same opinion, and has taken particular pains to prove 

 that rain-water always contains a very minute quantity of carbonate 

 of ammonia. 



To this cause, which must have the effect of infusing an azotized 

 principle into the tissues of plants, must be added another, which is 

 perhaps not the least energetic. It is this, that under certain elec- 

 trical influences, of which M. Becquerel has made a particular study, 

 hydrogen in the nascent state, in contact with azote, may actually 

 give rise to ammonia. By means of this view, it becomes easy to 

 conceive how non-azotized organic substances, under the mere in- 

 fluence of the putrid fermentation, might give origin to ammoniacal 

 salts, which would then exercise a fertilizing action on the soil. 



During the growth of plants, a portion of the w^ater absorbed by 

 the roots is evidently assimilated ; and this circumstance enables us 

 to conceive the formation of many of the immediate principles of 

 vegetables, the chemical composition of which is precisely repre- 

 sented by carbon and the elements of water ; such as starch, sugar, 

 etc. We can also understand the presence of those principles, 

 which have further a certain proportion of oxygen in excess, inas- 

 much as we have ascertained that during the decomposition of car- 

 bonic acid by the green parts of vegetables, the whole of the oxygen 

 is not eliminated. But there are substances elaborated by plants 

 which, with reference to oxygen, contain a quantity of hydrogen 

 much greater than is requisite to form water ; such are the resins 

 and other carburets of hydrogen in the cone-bearing trees, and the 

 fat oils in the oleaginous seeds. This excess of hydrogen led several 

 physiologists to conclude that water was decomposed in the course 

 of vegetation, — that there was fixation of its hydrogen and disen^ 

 gagement of its oxygen gas. 



* Piobert, M6m. de I'Academie de Metz, 1837. 



6 



