1908] HARVEY—PRAIRIE-GRASS FORMATION 279 
the chresard at a minimum are thus the ecological conditions which 
strongly mark the serotinal floral aspect. 
SPECIES OF THE SEROTINAL FLORAL ASPECT 
Factes.—Bouteloua oligostachya,t B. hirsuta,t B. curtipendula,} Bulbilis 
dactyloides.*+ 
MARY SPECIES.—Kuhnistera purpurea,t Verbena stricta,*{ Ratibida 
columnaris,*; Kuhnistera candida,j Symphoricarpus occidentalis,*} Amorpha 
canescens.*t} 
SECONDARY SPECIES.—Agropyron occidentale, Carduus undulatus,* Euphor- 
bia marginata,* Hymenopappus filifolius, Calamovilfa longifolia, Polygala alba.* 
TERTIARY sPECIES.—Lygodesmia juncea, Lacinaria squarrosa, Brauneria 
Pallida,* Meriolix serrulata,* Eriocarpum spinulosum, Erigeron ramosus,* 
Potentilla Hippiana.* 
RUDERAL sPECIES.—Cassia chamaecrista, Onagra biennis, Amaranthus 
staecizans, Melilotus alba,* Chenopodium album, Lactuca canadensis, Apocynum 
cannabinum. : 
*From previous aspect. {Forming associations. 
_ Agropyron occidentale is the first of the serotinal grasses to bloom. 
Itis a xerophytic bunch-grass and occupies prairie crests, where it 
curs copiously, rarely even of facial rank. It is one of the pioneers 
of the bunch-grass stage and is associated with the Andropogons, 
Passing with these forms as they give place to the Boutelouas and 
being entirely absent in the older and more mesophytic prairie. In 
transitional stages from the bunch-grass open association to the less 
Xerophytic closed sod association, Agropyron .remains not infre- 
dtently in subcopious abundance as a relict of the earlier condition. 
The rootstock is here an efficient mode of propagation. 
The three grama grasses, Bouteloua hirsuta, B. oligostachya, and 
. curtipendula, which head out during the early days of July, enter 
upon anthesis almost simultaneously with the beginning of the 
“cond week of July, as does also the buffalo grass, Bulbilis dacty- 
loides. The Boutelouas are pioneer sod-formers, following only the 
buffalo 8rass, which as the pioneer sod-former encroaches upon the 
bunch-grasses, replacing them and preparing the way for the Boute- 
“Uas Which invariably follow closely. To the west, where the rainfall 
$ much less, Bulbilis is the prominent sod-former and is the fodder 
S488 of the great cattle ranges west of the Missouri. In our region 
't occurs along the xerophytic exposures of the bluff line, and as a 
