428 Transactions. — Botany. 



fraction in point of bulk, what could be more natural than the 

 supposition that their laitrogen also was derived from the same 

 source? For by this time it was well known that nitrogen 

 gas, in a free or uncombined state, constitutes four-fifths by 

 volume of the air. Observation of the behaviour of growing 

 plants, however, soon made it doubtful if this supposition 

 could be entertained ; and in the early years of the present 

 century Theodore de Saussure, a distinguished Swiss savant, 

 as the result of numerous experiments, concluded, not without 

 due caution, that plants do not fix and assimilate the free 

 nitrogen of the air, or get any part of their supply from that 

 source. 



The question thus raised continued to be debated for many 

 years ; but no certain results were gained until the investiga- 

 tion of the points in dispute were undertaken by the justly- 

 celebrated French savant Boussingault. In a series of careful 

 and masterly researches carried out between the years 1845 

 and 1865 Boussingault displayed remarkable ingenuity in de- 

 vising methods of interrogating nature by simple and decisive 

 experiments, and laid the foundation of the experimental 

 methods of to-day, which will be referred to in some detail 

 in the course of this address. His researches showed con- 

 clusively that, under the conditions of his experiments, 

 atmospheric nitrogen is not employed in the process of the 

 assimilation of plants. His experimental plants in every case 

 grew vigorously, and produced a normal amount of proteid 

 compounds when he presented to their roots nitrogenous com- 

 pounds of various kinds, in addition to the other non-nitro- 

 genous substances necessary for their nutrition. They grew 

 very badly, on the other hand, and their proteid substances 

 did not increase in amount, when this supply of nitrogenous 

 compounds was withheld, although the free nitrogen of the 

 air was at their disposal if they could use it. Thanks to the 

 now much further developed art of nourishing plants arti- 

 ficially, and especially by means of water cultures, we are to- 

 day in a position, by means of simple experiments, to afford 

 ocular demonstration of the important results obtained by 

 Boussingault. Whenever a sufficient quantity of saltpetre is 

 added to the nutritive solution the experimental plants grow 

 vigorously, produce numerous ripe seeds capable of germina- 

 tion, and give on analysis a corresponding increase in the 

 nitrogenous substances they contain. On the other hand, if 

 the nitrate is withheld from the nutritive mixture, the experi- 

 mental plant grows for a time, it is true, making use of the 

 proteid substances already contained in the seed for the 

 formation of the protoplasm of its cell and organs ; and this 

 stunted growth may even continue for some time, since the 

 protoplasm of the first leaves is again dissolved and absorbed 



