30 



MYCOLOGY 



(Fig. 9). The presence of these bacteria causes the formation of swell- 

 ings, tubercles, or nodules on the roots of the leguminous plants. Here 

 Bacillus radicicola remains, utilizing free atmospheric nitrogen until 

 about the time of flowering of the host, when it begins to assume in- 

 volution forms, enlarging considerably and assuming S-shaped or 

 Y-shaped forms (Fig. i o) . Then they are gradually absorbed by the 



""*>§»**' 







Fig. 9. — Cells of root tubercle of Lupinus angustifolius magnified to show the 

 bacteria; four cells with nuclei. {After Moore, Geo. T., Yearbook U. S. Dept. Agric, 

 1902, 'pi. xxxix.) 



green leguminous plants and their substance is transformed into a 

 form of nitrogenous substance, which is utilized by the leguminous 

 host, either as food, or stored as nitrogenous reserve supplies. The 

 nodule becomes emptied of its contents and remains as a hollow sac, 

 enough of the organisms being returned to the soil to seed it and provide 

 for infection of other leguminous crops that may follow. The growth 



