212 Bacteria in Relation to Country Life 



bination within the soil in which it is available to the 

 higher plants — at any rate, to members of the Papiliona- 

 ceous family. At the same time, it will be granted that 

 further confirmation is essential before such a conclusion 

 can be accepted as fully established." 



The further confirmation was not lacking, and was 

 soon brought forward by numerous investigations, 

 among them those begun at Rothamsted in 1888. 

 The failures of the earlier experiments were also explained 

 since the artificial soils used there precluded the entrance 

 or development of the bacteria. 



Nodules on the roots of legumes. — The discovery of 

 Hellriegel and Wilfarth demonstrated that legumes 

 possess the power of acquiring the free nitrogen of the 

 •air, owing to the bacteria which form the nodules on their 

 roots. Without the bacteria and the nodules, they lack 

 this power. However, these investigators were not the 

 first to observe that nodules are present on the roots of 

 leguminous plants. We have reason to think that these 

 swell'ngs or nodules had been observed centuries ago. 

 The ItaUan, Malpighi, described them in 1687. They 

 appeared to him as galls. 



In 1866 it was demonstrated by the Russian botanist, 

 Woronin, that the nodules are filled with great numbers 

 of bacteria, and, subsequently, it was shown by others 

 that besides the bacteria there are certain filaments or 

 threads which appear to pass from cell to cell. These 

 filaments are much like hollow tubes widening out to 

 funnel-shaped forms where they come in contact with 

 the cell-walls. It is apparently their function to create 

 a passage through which the bacteria pass from cell to cell. 



