206 



BOTANY OF THE LIVING PLANT 



Experiments have shown that Leguminous seedHngs grown in 

 steriHsed sand, to wdiich a full food-supply exclusive of combined 

 nitrogen has been added, fail from want of nitrogen. Like any other 

 green plants they are unable to use the free nitrogen of the air. But 





^ 



A 





'A/ 



Fig. 156. 

 Young tubercles (A') on a root (W) of Vicia Faba. Z? = large- celled tissue filled 

 with masses of Bacteria. 3/ = meristem. T = tracheides. ( x 60.) 2, a cell infected 

 with bacteria, and smaller non-infected cells. ( >; 320.) 3, an infected root -hair. 

 ( X 320.) 4, Bacterioids. 5, unaltered Bacilli. ( x 1200.) (After Strasburger.) 



if a water-extract of ordinary soil be made,^ — especially if the soil has 

 lately grown similar Leguminous plants, — and if it be added to the 

 culture, the plants will thrive with all the evidences of a sufficient 

 nitrogenous supply, while a free development of tubercles takes place 

 upon the roots. Moreover, analysis show^s that the nitrogenous 

 content of the tuberculous plants is increased by the co-operation of 

 the two organisms. But it is still uncertain how this is done. It 



