34 2 The Physiology of Plants BOOK m 



out. He was so firm in holding this opinion that he said 

 he failed to find in these lupin cultures any satisfactory 

 evidence of fixation of atmospheric nitrogen, a denial which 

 he repeated in 1876 and again in 1883, though evidence 

 in the opposite direction was slowly accumulating. 



In the years 1879-81 Deherain found that under crops 

 of sainfoin the nitrogen of the soil increased in spite of 

 the removal of large amounts in the crops, an observation 

 confirmed later (1883) by Lawes and Gilbert in the case of 

 clover. 



That these strange results must be associated definitely 

 with the leguminous plants seems to have been first clearly 

 comprehended by Schultz-Lupitz, after a number of trials 

 which extended over fifteen years. For this period he 

 cultivated lupins on the same soil without supplying them 

 with any combined nitrogen and found the yield about 

 the same year after year, while in other experiments the 

 lupin crop materially improved the soil for a cereal crop 

 following it. Analysis of the soil at the beginning and end 

 of the fifteen years showed a substantial increase of its 

 content of combined nitrogen. He published his results 

 in 1881. 



It is, however, mainly to the researches of Hellriegel 

 and Wilfarth, and to a less extent to those of Lawes and 

 Gilbert, that we owe the elucidation of the matter. 



Hellriegel and Wilfarth published in 1886, and more fully 

 in 1888, a comprehensive account of the researches they 

 had conducted during several years with peas and other 

 leguminous plants, oats, and barley. They cultivated some 

 of each in pots in washed quartz sand which had been 

 carefully sterilized, and supplied them with a nutritive 

 solution containing no combined nitrogen. Others were 

 supplied also with nitrate of soda in varying quantities. 

 Others were watered with a small quantity of an extract 

 of arable soil. The results showed that with the cereal 



