48 ROOT DEVELOPMENT IN THE GRASSLAND FORMATION. 



well supplied with unbranched laterals seldom over an inch in length. In 

 fact most of them have an extent of less than 0.5 inch. Here, again, is a 

 widely spreading but relatively shallow root system. 



Asclepias arenaria. — This milkweed, while seldom occurring in great abun- 

 dance, is a widely distributed component of mixed-prairie vegetation of the 

 sandhills. Three specimens were examined on a fairly well covered hillside. 

 The plants were about 2 feet high and in blossom. One tap-root gave rise to 

 two stems, the others each to one, at depths of 6 and 8 inches respectively. 



Fig. 18. — Root system of Asclepias arenaria. 



