556 



greater, and in one case more than 30 times as great, when a supply 

 of combined nitrogen was provided. The evidence is therefore suffi- 

 ciently clear that all the conditions provided, apart from those which 

 depended upon a supply of combined nitrogen, were adapted for 

 vigorous growth ; and that the limitation of growth where no com- 

 bined nitrogen was supplied was due to the want of such supply. 



In 2 out of the 4 experiments with cereals in 1857, there was a 

 slight gain of nitrogen beyond that which should occur from error 

 in analysis ; but in no one of the 6 in 1858, when glazed earthenware 

 instead of slate stands were used, was there any such gain. It is con- 

 cluded, therefore, that there was no assimilation of free nitrogen. 

 In some cases the supply of combined nitrogen was not given until 

 the plants showed signs of decline ; when, on each addition, increased 

 vigour was rapidly manifested. In others the supply was given 

 earlier and was more liberal. 



As in the case of the leguminous plants grown without extraneous 

 supply of combined nitrogen, those grown with it progressed much 

 less healthily than the graminaceous plants. But the results under 

 these conditions, so far as they go, did not indicate any assimilation 

 of free nitrogen. 



The results of experiments with plants of other descriptions, in 

 which an extraneous supply of combined nitrogen was provided, also 

 failed to show an assimilation of free nitrogen. 



Thus, 19 experiments with cereals, 9 without and 10 with an ex- 

 traneous supply of combined nitrogen 6 with leguminous plants, 

 3 without and 3 with an extraneous supply of combined nitrogen, 

 and also some with other plants, have been made. In none of the 

 experiments, with plants so widely different as the graminaceous and 

 the leguminous, and with a wide range of conditions of growth, was 

 there evidence of an assimilation of free nitrogen. 



The conclusions from the whole inquiry may be briefly summed 

 up as follows : 



The yield of nitrogen in the vegetation over a given area, within a 

 given time, especially in the case of leguminous crops, is not satis- 

 factorily explained by reference to the hitherto quantitatively deter- 

 mined supplies of combined nitrogen. 



The results and conclusions hitherto recorded by different experi- 



