206 



BOTANY OF THE LIVING PLANT 



Experiments have shown that Leguminous seedlings grown in 

 sterilised sand, to which 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 



FIG. 156. 



Young tubercles (K) on a root (W) of Vicia Faba. S= large-celled tissue filled 

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

 with bacteria, and smaller non-infected cells. ( x 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 shows 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 



