298 



SYMBIOTIC NITROGEN FIXATION 



The alfalfa organism is the most sensitive of the legume bacteria 

 to acidity and conversely the lupine organism is the most resistant to 

 acidity. 



FIG. 36 



FIG. 37 



FIGS. 36 and 37. Ash-agar plate from bean (Phaseolus vulgaris), showing giant 

 colonies in a thickly seated plate. Ash-agar plate from perennial pea (Dathyrus 

 latifohus) ; the clear spaces are due to sterilized fluid carried over with pieces of 

 nodule tissue. (After Burrill and Hansen). 



