2l6 



BOTANY OF THE LIVING PLANT 



a centra] mass of enlarged cells, crowded with bacteria which do 

 not, however, destroy the nucleus or other parts of the host cell 

 (Fig. 104, 1, 2). Vascular strands traverse the outer tissues of the 

 nodule and connect up with the stele of the root, while the presence 



K 





Jd 



* * a? 







S 



Fig. 164. 



1. Young Nodules (K) on a root (W) of Vicia Faba. B=large-celled tissue filled 

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

 with Bacteria, and smaller non-infected cells. ( x 320.) 3, an infected root-hair. 

 ( ■' 320.) 4, Bacteroids. 5, unaltered Bacilli. (X1200.) (After Strasburger.) 



of a meristem at the apex of the nodule provides for its continued 

 growth. The bacterium (known as Bacillus radicicola) exists in the 

 soil in a motile condition and penetrates the root-hairs of suitable 

 leguminous plants. Inside the root-hair the bacterium multiplies 

 very rapidly, and in the form of an " infection thread " advances 

 along the hair (Fig. 164, 3), penetrating a group of cortical cells, 

 which begin to divide, and the nodule is thus originated. The bacteria 



