ON THE GROWTH OF LEGUMINOUS CROPS. 49 



supposition that the gains were due to the absorption of combined 

 nitrogen from the atmosphere, an objection to such a view is, that it 

 would not explain the circulation of nitrogen in nature ; and his main 

 conclusion is, that there are two actions going on within the soil, one 

 liberating nitrogen, and the other bringing it into combination, the 

 latter favoured by vegetation. 



Upon the whole, then, it would seem, that the losses found by 

 Frank may be explained by the special conditions of the experiments 

 themselves ; whilst the gains, if not to be accounted for by sources of 

 error incidental to experiments made in free air, can only be explained 

 by fixation in some way. 



The most remarkable of the results indicating the fixation of free 

 nitrogen are those of Professor Hellriegel and Dr. Wilfarth. Hellriegel 

 found that whilst plants of the Gramineous, the Chenopodiaceous, the 

 Polygonous, and the Cruciferous families, required combined nitrogen 

 to be supplied within the soil, Papilionaceous plants did not depend 

 on such soil-supplies. 



Peas, sown in washed sand with nutritive solutions free from 

 nitrogen, generally failed, but occasionally grew luxuriantly ; and root- 

 nodules were always developed coincidently with luxuriance, but not 

 without it. But when to the non-nitrogenous sandy matrix, a few c.c. 

 of the watery extract of a rich soil were added, the luxuriance was 

 always marked, as also was the development of the root-nodules. 

 Lupins, however, failed when treated in the same way, but succeeded 

 when the soil was seeded by a watery extract of a sandy soil where Lupins 

 were growing well, and root-nodules were then abundantly produced. 



The amounts of produce recorded seemed to leave no doubt that 

 they contained much more nitrogen than was supplied in the seed; 

 whilst the amount added in the soil-extract was quite immaterial. 

 The negative result with Graminese, with Peas under sterilised con- 

 ditions, or in sand not seeded with rich soil-extract, and with Lupins 

 in sand not seeded, or seeded with the rich soil-extract, and, on the 

 other hand, the positive result with Peas in the seeded sand, and with 

 Lupins when the sand was seeded with an extract from a suitable soil, 

 seemed to exclude the supposition of any other source of gain than the 

 fixation of free nitrogen under the influence of micro-organisms ; and 

 Hellriegel was disposed to connect the action with the root-nodules and 

 their contents. 



Wilfarth gave the results of a subsequent season's experiments, 

 which fully confirmed those recorded by Hellriegel, both as to the 

 negative result with other plants, and to the positive result with 

 Papilionacese. Peas grew luxuriantly when the nitrogen-free soil was 

 seeded with the watery extract from any cultivated soil, but Serradella 

 and Lupins, only when seeded with an extract from soil where these 

 plants were growing. 



In four experiments with Lupins, nearly 50 times as much dry 

 substance was produced, and nearly 100 times as much nitrogen was 

 assimilated, with, as without, seeding with the soil-extract ! 



G 



