FLORAL SUCCESSION IN THE PRAIRIE-GRASS FORMA- 

 TION OF SOUTHEASTERN SOUTH DAKOTA 



SEROTINAL AND AUTUMNAL FLORAL ASPECTS 



CONTRIBUTIONS FROM THE HULL BOTANICAL LABORATORY 117 



LeRoy Harris Harvey 



(with four figures) 



Serotinal floral aspect 



Climatologically and florally the serotinal is perhaps the most 

 distinctly demarked of the aspects. The climatological changes 

 which set it off from the estival are quite generally appreciated, while 

 the general blooming of the pioneer sod-formers during the early 

 part of July with the accompanying serotinal bloomers no less dis- 

 tinctly marks it in a floral way. 



One records now less dissimilarity in aspect and tone on crest, 

 slope, and base; the more open association, however, still marks the 

 crest. The tone is determined by the dull-greenish vegetative stalks 

 of Solidago rigida and Helianthus Scaberrimus, which occur copiously 

 throughout the formation. It is relieved locally on lower slopes by 

 the yellow of Ratibida columnaris and on upper slopes by the blue 

 of Verbena stricta and the canescence of Amorpha; while Meriolix 

 serrulata, Brauneria pallida, Potentilla Hippiana, Erigeron ramosus, 

 Poly gala alba, and Euphorbia marginata, all of which extend over 

 from the estival, are less influential. A few conspicuous forms are 

 added in this aspect, but never of sufficient abundance to strongly 

 variegate the dull green of the tone given by the leafy stems of Soli- 

 dago and Helianthus. 



The general flowering of Agropyron occidentale, Bulbilis dacty- 

 loides, and the Boutelouas, together with Kuhnistera purpurea and K. 

 Candida, distinctly marks the inception of the serotinal aspect, which is 

 characterized by the gradual appearance of few but conspicuous 

 bloomers and the attainment of maximum flowering of late estival 

 forms, rather than by the addition of numerous forms as in the 



277] [Botanical Gazette, vol. 46 



