98 BOTANICAL GAZETTE [AUGUST 
remarkable for the general flowering of Poa pratensis. P. compressa 
is associated, but occurs sparsely and principally upon the upper 
slopes. The relative place of these two forms has been hard to deter- 
mine, but it seems that P. compressa occurs as a forerunner of the 
bluegrass. In its distribution P. pratensis is confined to depressions 
and lower slopes, and is always indicative of the highest soil-water 
content, the most favorable exposure, and richest humus. In these 
situations it forms a dense sod, frequently exclusive, which is con- 
stantly pushing up the slopes replacing the bunch-grasses, outlying 
individuals frequently reaching the higher slopes. It is perhaps one 
of the most mesophytic of prairie forms, and is almost invariably the 
forerunner of the prairie shrubs, Symphoricarpus occidentalis 
Rhus glabra. It reaches its highest development on the northwest 
exposure, and it is up this exposure that the flood-plain and ravine 
forest of this region has made its greatest advance upon the prairie. 
Poa is the first facies to bloom, but as noted above is of restricted 
distribution. It isa perennial and propagation is rapid by the abul- 
dant rootstocks, which leads to dense sod. 
With the bluegrass are successively added Ovxalis stricta, Linum 
rigidum, and Polygala alba. Never very abundant and of low 
stature, they add but little to the tone of the aspect, as they are OV 
topped by the oncoming facies of later aspects. Oxalis appears ? 
lower slopes, possessing frequently a gregarious distribution. It may 
be either annual or perennial. The few seeds are restrictedly dis- 
persed by the dehiscing capsules. Linum is a decidedly xerophytic 
annual, being a relict of earlier stages. It appears in the open 59 
ciation on the upper slopes and along prairie crests. It is mee 
common and its fugacious petals prevent all but entire inconspicu- 
ousness. Its seeds are few and their mobility little. Polygala 
sparingly distributed over the lower slopes of prairie knolls, always 
working up to higher positions with the increase of mesophyti¢ 
conditions, but it never remains in the Poa sod. It is perhaps - 
of the best indices of progressive mesophytism among the prairie 
species. It is a perennial from woody rootstocks. Seeds are borne 
two in a capsule and migration is very slow. : 
As the vernal floral aspect is drawing to a close, several minor 
elements bloom, extending vernal floral activity over into t 
he first 
| 
| 
