161 



floating- in the air and were deposited in the pots in which the plants 

 grew. As a rule, the greater the abundance of tubercles the more 

 vigorous were the plants and the greater the gain in nitrogen. The 

 gain of nitrogen froin the air by the legumes explains why they act as 

 renovating crops. (Agr. Sci., Vol. IV, p. 22.) 



From some careful experiments by A. Petermann on yellow lu})ins 

 (Li/ pi /I lis hitei(s) the author concludes that the physiological role of 

 the tubercles must not be exaggerated. They can not be the only 

 cause of the fixation of nitrogen, although their presence may explain 

 why the intervention of atmospheric nitrogen is most marked in the 

 case of the Leguminosse. He further shows that sodium nitrate is not 

 injurious, but beneficial, to lupins. The trouble in its use results 

 niostlj'^ from the fact that it is very soluble and is soon washed down 

 by the rain out of the reach of the roots, which must then draw their 

 nitrogen from the atmosphere by means of the microbic organisms. 

 (Agr. Sci., Vol. IV, p. 264.) 



Pagnoul has measured the loss and gain of nitrogen by the soil as 

 the result of the cultivation of special crops. He sowed grass and 

 clover in four pots, but left two others Avithout any crop. The gain 

 of nitrogen permanently fixed in the soil in one year — March, 1888, to 

 March, 1889 — was as follows: With no crop the soil gained at the 

 rate of 29 kilograms per hectare per year, with the grass crop 394 

 kilograms, and with the clover crop 904 kilograms. On the other 

 hand, the total proportion of nitrogen removed from the soil by the 

 drainage water was in each case as follows: No crop, 85; grass, 5; 

 clover, 18. (Agr. Sci., Vol. IV, p. 325.) 



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