1908I HARVEY— PRAIRIE-GRASS FORMATION 107 



immobility and high ecological demands result in its gregarious 

 habit. The berries are persistent and birds may help somewhat in 

 dispersal. 



The last of this group to bloom is Verbena stricta. About June 

 25 the purplish-blue flowers make their appearance at the base of the 

 long (15-30'^"^) indeterminate terminal spikes in a narrow band, which 

 moves upward day by day at the rate of about i to 2^^^". The maxi- 

 mum flowering, however, seems to be reached about July 10 to 20. 



Fig. 3. — Late estival aspect; Verbena stricta determining the tone of a lower 

 slope; the white patches are the ruderal Hordeum jubatum. 



Like Ratibida and for the same reason, it flowers abundantly through 

 July and August and into September. It has a copious and general 

 distribution and not infrequently assumes a dominating influence 

 upon lower (fig. j) and upper slopes as well as crests. It is a per- 

 ennial from a heavy root and several stalks from the same root give 

 it not infrequently a "bunch" appearance. 



During the last days of June and the first days of July, several 

 forms appear to complete the estival floral aspect. In order of 

 flowering they are Acerates viridiflora linearis, Potentilla hippiana, 

 Euphorbia marginata, and Aviorpha canescens. All assume local 



