46 



ROOT DEVELOPMENT IN THE GRASSLAND FORMATION. 



only 0.1 to 0.2 foot or slightly deeper and nearly parallel to the soil surface. 

 The latter may end in the first 0.5 to 1 foot of soil at distances of 1 to 2 feet 

 from the plant (fig. 15). Beginning in the second inch of soil, the roots are 

 exceedingly well branched. These branches are very fine; the older ones are 

 black and the younger ones lighter in color. They vary from a millimeter to 

 8 centimeters in length. While some are only slightly branched, others are 

 branched to the second or third order. The working depth is 3.2 feet. Thus 

 this grass is well fitted for absorption in the surface 2 or 3 feet of soil for a dis- 

 tance of 1 to 1.7 feet on all sides of the clump. 



Erigeron bellidiastrum. — This subdominant, much-branched annual fre- 

 quently forms extensive societies in the sandhills. At this station the plants 

 were very abundant, 1 to 1.2 feet high, and in full bloom. All of the eight 

 specimens examined had tap-roots from 2 to 5 mm. in diameter, which tapered 

 so rapidly that at a depth of a foot they were never over 1 or 2 mm. thick. 

 Beginning about an inch below the surface, branches come off in great profu- 

 sion. The largest of these, which are usually 3 to 7 in number, varying with 



Fig. 16. — Erigeron bellidiastrum. 



the size of the plant, are only 1 to 2 mm. in diameter, while the others are 

 much smaller, some being hairlike. Most of the larger ones run off in a direc- 

 tion more or less parallel with the soil surface for distances of 0.7 to 1.7 feet 

 before turning downward. While some of these end without descending below 

 the first foot, other branches were traced to depths of 2.5 feet (fig. 16). The 

 tap pursues a more or less devious downward course, but seldom meanders 

 more than a foot horizontally from the base of the crown. Both the tap and 

 larger laterals are abundantly supplied with threadlike, mostly unbranched, 



