300 



SYMBIOTIC NITROGEN FIXATION 



" Buried colonies are small and submerged, most frequently lens, 

 or spindle-shaped, with smooth and even edges. They are rather 

 opaque, granular in structure, and in color are cream to a chalk 

 white. They increase slowly in size, eventually appearing on the 



FIG. 39. Young nodule, showing the beginning of the differentiation of its tissues. 



(After Prazmowski.) 



surface of the agar as surface colonies, when the growth becomes 

 rapid. The lens colonies, however, remain visible for many days in 

 the center of the new growth. 



"Surface colonies originate at or near the surfaces of the agar or 

 develop from buried colonies. They are drop-form, watery, muci- 



