130 ROOT DEVELOPMENT IN THE GRASSLAND FORMATION. 



those on the low ground, while the tops were equally well developed. These 

 differences in root habit namely, a deep tap-root with no major branches and 

 relatively few smaller ones in one habitat, and a pronounced wide-spreading 

 shallower root system with a smaller development of the tap-root in the other, 



Fig. 35. — Root system of Mcdi- 

 cago sativa, 2.5 months old. 



Fig. 36. — Root system of Melilotus alba about 

 4 months old. 



must be attributed to soil conditions with their resultant effect upon water- 

 content, soil solutes, and perhaps aeration. Which of these or what com- 

 bination of these is the controlling one can be definitely answered only by a 



