TRANSACTIONS OF SECTION B. 



6 £5 



now described, will, it is hoped, shortly appear in the Journal of the Chemical 

 Society of London. 



3. On the Assimilation of Atmospheric Nitrogen liy Plants. 

 By Professor W. O. Atwater. 



Plants (dwarf peas) were cultivated in purified sand to which were added 

 nutritive solutions with known quantities of nitrogen in forms of potassium and 

 calcium nitrates. The amounts of nitrogen supplied in solution and seed were com- 

 pared with amounts found at the end of the experiment in residual solution and 

 plants. The excess of the latter over the former must represent nitrogen acquired 

 from the atmosphere. 



A number of trials were made, with varying degrees of concentration of the- 

 nutritive solutions, with different amounts of food per plant, and with larger and 

 smaller supplies of nitrogen in the solution ; the object being to test tbe effect of 

 normal and abnormal conditions upon the acquisition of atmospheric nitrogen by 

 tbe plants. In concentrated solutions, which are known to be prejudicial to 

 assimilation, the plants acquired little or no nitrogen from the air. 



In the moderately dilute solutions, however, wbose concentration was such as 

 has elsewhere been found favourable to healthy growth, the nitrogen of the plants 

 largely exceeded that supplied by nutritive solution and seed, and is shown by the 

 following figures : — 



That is to say, in four trials with solutions sufficiently dilute to permit normal 

 assimilation, the very poorly fed plants obtained over one-third, and the tolerably 

 well fed ones, one-half, their whole nitrogen from the atmosphere. 



The plants acquired a milligramme of nitrogen from the air, for every milligramme 

 taken from the solution and seed. And what is even more noticeable, not only 

 where the amount of nitrogen supplied was very small did they do this, but also 

 where it was more than twice as large. The results show very clearly that the- 

 assimilation of nitrogen decreased with the concentration of the solution, and with 

 the reduction of the sxvpply of total food, or of nitrogen in the food. In other 

 words, the acquisition of aerial nitrogen was greater in proportion as the conditions- 

 of growth were more nearly normal. This fact is of interest in view of the cir- 

 cumstance that the experiments upon which the belief that plants acquire little or 

 no free nitrogen from the atmosphere is based, have been made under conditions- 

 more or less abnormal. 



The experiments do not show whether the nitrogen acquired from the atmos- 

 phere was combined or free nitrogen. It is, however, very difficult to believe 

 that so much nitrogen could have been gathered from the nitrogen compounds,, 

 ammonia, nitrates, nitrites, &c, of the atmosphere. 



