Fixation of Nitrogen. 



201 



similar in appearance and size to those found on beans. 

 The size of the nodules depends on the number on the 

 plant. When few, the nodules are likely to be large, when 

 more numerous the size is smaller. The total mass of 



FIG. 20. TUBERCLES ox SOY BEANS. 

 B. the roots are free from tubercles; C. the roots 

 are studded with large tubercles. Large masses 

 of them are to be seen on the main root. 



the nodules may make up one fourth of the weight of the 

 root system. 



On cutting the nodules open it will be found that the 

 color of those that are small is pale red or pink, unlike 

 the color of any other part of the plant. If a little of 

 the content of the nodule is examined under the micro- 



