THE SHORT-GRASS PLAINS. 



139 



uriant and less mixed, and the growth-form is smaller as a rule. It is also 

 significant that most of the societies are found in the eastern half with a rain- 

 fall above rather than below 15 inches. In the western portion the societies 

 are better developed in the valleys and along the lower slopes, and are much 

 reduced in number and dominance on the upland. 



Prevernal Societies. 



Carex pennsylvanica. 

 Antennaria dioeca. 

 Anemone patens. 

 Leucocrinum montanum. 

 Androsace occidentalis. 

 Draba caroliniana. 



Vernal Societies. 



Astragalus crassicarpus. 

 Aragalus lamberti. 

 Erysimum asperum. 

 Fragaria virginiana. 

 Viola pedatifida. 

 Comandra umbellata. 

 Vicia americana. 

 Anemone cylindrica. 

 Sieversia ciliata. 

 Achillea millefolium. 

 Hosackia americana. 

 Sophora sericea. 

 Senecio aureus. 

 Sisyrincbium augustifolium. 

 Lithospermum linearifolium. 

 Castilleia sessiliflora. 

 Astragalus drummondii. 

 Krynitzkia virgata. 

 Agoseris cuspidata. 



Estival Societies: 



Psoralea tenuiflora. 

 Petalostemon candidus. 

 Petalostemon purpureus. 

 Amorpha canescens. 

 Psoralea argophylla. 

 Brauneria pallida. 

 Glycyrhiza lepidota. 

 Lepachys columnaris. 

 Erigeron ramosus. 

 Tradescantia virginiana. 

 Polygala alba. 

 Lupinus ornatus. 

 Astragalus bisulcatus. 

 Astragalus adsurgens. 



Estival Societies — continued. 

 Delphinium menziesii. 

 Yucca glauca. 

 Helianthus rigidus. 

 Monarda citriodora. 

 Malvastrum coccineum. 

 Erigeron pumilus. 

 Rosa arkansana. 

 Hymenopappus tenuifolius. 

 Opuntia mesacantha. 

 Opuntia polyacantha. 

 Dalea laxiflora. v 

 Meriolix serrulata. 

 Linum rigidum. 

 Phlox douglasii. 

 Pentstemon grandiflorus. 

 Pentstemon gracilis. 

 Aster ericoides. 

 Gaura coccinea. 

 Astragalus mollissimus. 

 Gilia pungens. 

 Gilia aggregata. 

 Verbena stricta. 

 Verbena hastata. 

 Lygodesmia juncea. 

 Hedeoma drummondii. 

 Steironema ciliatum. 

 Castilleia integra. 

 Rudbeckia hirta. 

 Haplopappus spinulosus. 

 Psoralea cuspidata. 

 Balsamorhiza sagittata. 



Serotinal Clans: 



Solidago rigida. 

 Solidago missouriensis. 

 Aster multiflorus. 

 Artemisia frigida. 

 Artemisia cana. 

 Grindelia squarrosa. 

 Gutierrezia sarothrae. 

 Senecio douglasii. 

 Artemisia filifolia. 



Serotinal Societies — continued. 

 Liatris punctata. 

 Chrysopsis villosa. 

 Carduus undulatus. 

 Artemisia dracunculoides. 

 Artemisia gnaphalodes. 

 Artemisia canadensis. 

 Kuhnia glutinosa. 

 Eriogonum annuum. 

 Thelesperma gracile. 

 Thelesperma trifidum. 

 Eriogonum micro thecum. 

 Eriogonum alatum. 

 Solidago speciosa. 

 Liatris scariosa. 

 Liatris pycnostachya. 

 Gymnolomia multiflora. 



Vernal Clans: 



Delphinium penardi. 

 Pentstemon albidus 

 Specularia perfoliata. 

 Oxalis stricta. 

 Oxalis violacea. 

 Viola nuttallii. 



Estival Clans: 



Asclepias speciosa. 

 Asclepias verticillata pumila. 

 Lactuca pulchella. 

 Lathyrus ornatus. 

 Psoralea esculenta. 

 Potentilla pennsylvanica. 

 Evolvulus argenteus. 

 Dalea aurea. 

 Cactus viviparus. 

 Acerates viridiflora. 

 Allionia linearis. 

 Gerardia aspera. 

 Verbena bipinnatifida. 



Serotinal Clans: 



Solidago gramini folia. 

 Liatris squarrosa. 



THE SHORT-GRASS PLAINS. 

 BULBILIS-BOUTELOUA ASSOCIATION. 

 Nature. — The short-grass plains owe their distinctive impress to grama and 

 buffalo-grass. These are sod-formers with dense root systems. As Shantz has 

 shown at Akron (1911 : 33), the water below 12 inches is non-available for 

 much of the growing season, with the result that the roots are usually con- 

 fined to the first foot of soil. 1 A further consequence is that the short-grasses 

 mature in July. Thus, the soil beneath a short-grass cover is often without 

 available water below 18 inches, and the water-content in the upper foot is 

 low after mid-summer. As a consequence, the deeper-rooted tall-grasses and 

 subdominant herbs are practically excluded and the typical short-grass cover 

 is very uniform and monotonous as a result. 



>Cf. Weaver, 1919, 1920. 



