390 BOTANICAL GAZETTE © [JUNE 
groups, the one earlier, the other somewhat later, may be dis- 
tinguished, however. The former comprises Amorpha canescens, 
Kuhnistera candida, Psoralea floribunda, Solidago rupestris, S. rigida, 
Verbena stricta, V. hastata, etc.; the latter, Lacimtaria squarrosa 
intermedia, L. scariosa, L. punctata, Vernonia gigantea, Aster sericeus, 
and the aianthous bloomer, Aster multiflorus. 
The buffalo grass formation is characterized by two types, 
the Bulbilis type and the Bouteloua type. The geographical 
area of the former is large, but greatly interrupted, and, while 
the facies manifests great abundance, its frequence is not com- 
parable to that of Bouteloua oligostachya or Andropogon scoparius. 
The dense mats of buffalo grass render this formation fairly 
exclusive, except where it is interrupted. The number of sec- 
ondary species is small. They are for the most part reduced 
facies of adjacent formations, Aristida purpurea, Agropyron pseudo- 
repens, Distichlis spicata stricta, Koeleria cristata, and the ubiqui- 
tous Boutelouas. The ground-tone of the formation is com- 
municated to it by the buffalo grass. Asclepias pumila and Ver- 
bena bipinnatifida, though characteristic of this formation, have 
little effect upon it. Amorpha canescens, Kuhnistera candida, and 
Solidago Missouriensis are common in this as in the prairie grass 
formation. The fullest development of this formation is found 
in the Dakotas, and eastern Montana, from which it extends 
southward through Nebraska and Kansas. The Bulbilis type 
prevails, for the most part upon argillaceous table lands. On the 
other hand, the Bouteloua type is found over sandy stretches, 
and hence is characteristic of the transition area between the 
prairies and the sand hills.’ 
The sand hill formations are three, the bunch grass, the blow 
out and the sand draw formations. The first covers by far the 
larger portion of the sand hills, and sandy plains of region IIT; 
the other two are restricted to the topographic features from 
The facies is Boutelona oligostachya, replaced on the bottoms of long see 
by B. curtipendula. The former is scarcely less exclusive than Bulbilis in ssn 
situations, where it composes from 92 to 98 per cent. of the vegetation. In . 
sition area between regions II and III it admits a number of secondary species: 
as Solidago mollis, Lygodesmia juncea, Plantago Purshii, etc. 
such 
