ON THE GROWTH OF LEGUMINOUS CROPS. 51 



suggests whether the greater evaporation from the leaves of the latter 

 causes greater aeration of the soil. 



Here, then, the gain of nitrogen by the Leguminosse is explained 

 in a very different manner from that assumed by other recent 

 experimenters. It seems, however, that the undoubted fact, that the 

 Graminese, and other non-Papilionaceous crops, do not benefit by the 

 actions supposed, excludes the supposition that Wolffs results with 

 Papilionacese are to be so explained. It is true that, neither in the 

 growth of the Clover in ignited soil, nor in that of the sand-Peas in 

 the washed sand, were the conditions such as would seem favourable 

 for the presence, development, and agency of micro-organisms. But if, 

 in the experiments in free air, there was no accidental source of 

 combined nitrogen, it would seem that the influence of micro-organisms 

 is at least as probable as that of the actions which Wolff supposes. 



Professor Atwater made numerous experiments, both on the 

 germination, and on the growth, of Peas. In eleven out of thirteen 

 experiments on germination, more or less loss of nitrogen was observed. 

 In all but one out of fifteen experiments on vegetation, there was a 

 gain of nitrogen, which was very variable in amount, and sometimes 

 very large. As a general conclusion, he states that, in some of the 

 experiments half or more of the total nitrogen of the plants was 

 acquired from the air. 



He considers that germination without loss of nitrogen is the 

 normal process ; that loss, whether during germination or growth, is 

 due to decay, and therefore only accessory. Nevertheless, he goes into 

 calculations of some of his own results, showing, by the side of the 

 actual gains, the greater gains supposing there had been a loss of 15 

 per cent, of nitrogen, and the still greater gains if there had been a 

 loss of 45 per cent., as in an experiment by Boussingault under special 

 conditions. Further, he says that whilst actually observed gains are 

 proof of the acquisition of nitrogen, the failure to show gain only 

 proves non-fixation, if it be proved that there was no liberation. He 

 suggests that the negative results obtained by Boussingault and at 

 Eothamsted, may be accounted for by liberation ; though at the same 

 time he recognises that the conditions of the experiments excluded the 

 action of either electricity or microbes. It may be remarked that, in the 

 experiments both of Boussingault and at Kothamsted, any cases of 

 decay were carefully observed, and the losses found explained accord- 

 ingly ; and it may be confidently asserted that the conclusions drawn 

 were not vitiated by any such loss. 



Atwater concludes that his results do not settle whether the 

 nitrogen gained was acquired as free or combined nitrogen, by the 

 foliage, or by the soil. He considers, however, that, in his experiments, 

 the conditions were not favourable for the action either of electricity 

 or of micro-organisms ; and he favours the assumption that the plants 

 themselves were the agents. Lastly, he considers the fact of the 

 acquisition of free nitrogen in some way to be well established ; 

 and that thus facts of vegetable production are explained, which 



