40 SOURCE AND ASSIMILATION OF NITROGEN. 



CHAPTER V. 



On the Origin and Assimilation of Nitrogen. 



We cannot suppose that a plant could attain maturity, even in 

 the richest vegetable mould, without the presence of mattei 

 containing nitrogen ; since we know that nitrogen exists in 

 every part of the vegetable structure. The first and most im- 

 portant question to be solved, therefore, is : How and in what 

 form does nature furnish nitrogen to vegetable albumen, and' to 

 gluten, or to fruits and seeds 1 * 



This question is susceptible of a very simple solution. 



Plants, as we know, grow perfectly well in a mixture of char, 

 coal and earth, previously calcined, if supplied at the same time 

 with rain-water. Rain-water can contain nitrogen only in three 

 forms, as dissolved atmospheric air, as nitric acid, or as ammonia, 

 Now, the nitrogen of the air cannot be made to enter into combi- 

 nation with any element except oxygen, even by the employment 

 of the most powerful chemical means. We have not the slight- 

 est reason for believing that the nitrogen of the atmosphere takes 

 part in the processes of assimilation of plants and animals ; on the 

 contrary, we know that many plants emit the nitrogen which is 

 absorbed by their roots, either in the gaseous form, or in solution 

 in water. But there are on the other hand numerous facts, 

 showing, that the formation in plants of substances containing 

 nitrogen, such as gluten, takes place in proportion to the quantity 



* " It is certain," says Saussure, " from the experiments which have 

 been made on this point, that plants receive their nitrogen only from such 

 animal or vegetable extracts, or from such ammoniacal vapors as they may 

 find in the soil, or extract from the air. When plants are made to 

 vegetate by the aid of water in a confined atmosphere, we may presume 

 that the new parts can only obtain nitrogen at the expense of other parts 

 to which it had formerly been supplied." (De Saussure, page 190.) 



