l6 THEORIES ON THE ABSORPTION OF NITROGEN 



follows: " Upon the whole, in these experiments consider- 

 able nitrogen fixation took place. Firstly, in sands and 

 clayey soils, as well as in vegetable soil properly so-called, 

 when I experimented without vegetable matter being present ; 

 secondly, both in soil and plant together when vegetable 

 matter was present." 



It has thus been distinctly proved that at the period 

 which we have now reached, namely, 1886, or two years 

 before the appearance of the work of Hellriegel and Wilfarth, 

 to whom the honour of suppressing all doubt and controversy 

 was reserved through their remarkable experiments, the fact 

 was already established that these soils, with the micro- 

 organisms they contain, had the faculty of fixing atmospheric 

 nitrogen. 



Complete ignorance reigned, however, as to the mode of 

 life of these micro-organisms. They had never been isolated, 

 and consequently had never been seen. The unique power 

 of the Leguminosai of growing in a soil deprived of nitrogen 

 and of storing up nitrogen in their tissues had not yet been 

 explained, in spite of the fact that botanists had already 

 described the occurrence of nodules on the roots of 

 Leguminosie. 



Woronin, in 1886, was the first to record the innumer- 

 able corpuscles, which closely resembled bacilli, present in 

 the protoplasm of the nodule cells, and declared that these 

 bacilli manufactured food for the benefit of the plant as well 

 as for their own. No one ever thought, however, of estab- 

 lishing a relationship between the root nodules and nitrogen 

 fixation. 



This discovery was to be made by Hellriegel and Wilfarth 

 in 1888, and we shall analyse their memoir as briefly as 

 possible. Before doing so, however, let us sum up the 

 various conclusions which the authors drew from the 

 researches we have quoted. 



First of all they believed that the Leguminosas could fix 

 both the nitrogen and carbonic acid of the atmosphere; then 



