1908] HARVEY—PRAIRIE-GRASS FORMATION ‘Ql 
slopes of prairie knolls where the grasses are bunched and the asso- 
ciation more or less open, though rarely seen at the crests; it thus 
not infrequently exerts a subtone effect at short range. It is perennial 
by means of its geophytic root. With the elongation of its peduncle 
and spreading of its umbel in maturation during the last week of the 
aspect, it becomes more conspicuous and persists thus far into the 
vernal aspect. 
The beginning of the second week of the prevernal aspect sees 
Carex pennsylvanica in full bloom. It occurs copiously, extending 
well up to the crests of knolls, but more abundantly on lower slopes, 
yet never influences the tone of the aspect. In places Carex may 
assume almost facial rank, but always maintains a bunchy or isolated 
distribution, which, however, is quite general. The peculiar yellow- 
ish-green shade of its leaves and its yellow staminate spikes which 
appear after the stigmas make it conspicuous. It is a perennial of 
xerophytic tendencies, propagating itself by rootstocks and stolons. 
Carex is shortly followed by the flowering of Antennaria campes- 
des and with its white tomentose leaves, scapes, and papillate heads, 
. Sives a characteristic local tone to this floral aspect, even from a 
distance. It occurs usually gregariously, being one of the two mat- 
forming species of the formation, and is very generally distributed 
throughout, facilitated by its perfect adaptation to wind dispersal. 
The mats themselves may be isolated or gregarious, as many as twenty 
having been noted in a plat of 6454™, yet single mats frequently cover 
re ", averaging about 1000 plants to the square meter. Propaga- 
tion is by stolons and migration is centrifugal, with a slow but positive 
°ccupation. Mats unite and take complete possession of extensive 
oes yet it yields before Poa pratensis, in no way being able to 
old its own against this sod-forming mesophyte. 
oan Seainieg floral aspect of the formation is terminated by the 
Pe age of Ranunculus ovalis, Astragalus crassicar pus, and Draba 
ities: ‘as the end of the third week of April. They appear 
thr hipecs 2 simultaneously, but in no way contribute equally to 
pect. Draba occurs only where the soil is exposed and the 
a hence on upper xerophytic slopes, and appears to be 
Whenever a close association is formed. It is an annual 
marked xerophytic tendencies, its leaves being basal and heavily 
