A. Reaction by decreasing water-content, Grindelia in moister depressions and trails, wKere 

 it is replaced by Bouteloua, Akron, Colorado. 







?- ■ . . 



■,»-<30' *- : 



B. Reaction by increasing water-content, Polanisia trachysperma in a sand-draw, 

 Crawford, Nebraska. 



