24 BOOT DEVELOPMENT IN THE GRASSLAND FORMATION. 



inches nearest the tip. The roots vary from those that are fibrous, herba- 

 ceous, and only 0.5 mm. thick to those that are tough, woody, and 6 or 7 mm. 

 in diameter (fig. 6). While some descend vertically, the larger roots more 



Fig. G. — Roots and rhizome of Helianthus rigidus. 



