STRUCTURE OP THE FORMATION 87 



Monarda fistulosa. H. tuberosus. 



Nabalus asper. Helenium autumnale. 



Polygonum emersum. Kuhnia eupatorioides. 



Eragrostis pectinacea. Solidago rigida. 



Falcata pitcheri. S. rigidiuscula. 



Gentiana puberula. S. nemoralis. 



Gyrostachys cernua. S. canadensis. 



Helianthus maximiliani. Sporobolus asper. 



H. annuus. S. heterolepis. 



H. grosse-serratus. Vernonia fasciculata. 



H. giganteus. V. gigantea. 



The serotinal period begins during the last days of July 

 and continues with a gradual diminution of bloomers until 

 the close of the flowering season. Its arrival is made known 

 by the blossoming of such species as Solidago rigida and 8. 

 nemoralis in the high prairies and S. canadensis and Lacin- 

 iaria pycnostachya in the meadows. New species continue 

 to be added until the 15th of September, Aster asureus, A. 

 lems, and Solidago rigidiuscula being among the last. After 

 September 10, the decrease of bloomers in the aspect is very 

 noticeable, the field being left entirely to the asters, golden- 

 rods, blazing stars, sunflowers, and ironweeds. These au- 

 tumnal bloomers secure the same recognition in the florai 

 covering as the vernal bloomers, by analogous means, i. e., 

 appearing late in the year rather than early, when there is 

 little else of prominence in the floral covering. During the 

 early serotinal period the vegetative layer is extremely com- 

 plicated, since many of the estival flowers persist for a time, 

 besides sporadic aianthous bloomers. Of the forty-seven 

 bloomers of the period, twenty-eight are species of the Com- 

 positae. Accordingly, the aspect from beginning to end is 

 preeminently a composite one, the yellow of the goldenrods 

 and sunflov»'ers being varied with the blue and white of the 

 asters and the purple of the blazing stars and ironweeds. It 

 is interesting to note that one-half of the serotinal species 



