16 
BULLETIN 791, U. S. DEPARTMENT OF AGRICULTURE. 
low brush, as well as of other plants, especially deep-rooted species 
indicates, therefore, a retrogressive succession in the wheat-grass 1 
Section B of figure 6, in addition to showing that the roots of a 
healthy specimen of yellow brush may feed at a depth in excess of 
ij teet, emphasizes the interesting fact that small wheat grass 
