1908] HARVEY— PRAIRIE-GRASS FORMATION 91 



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- 

 tris, and with its white tomentose leaves, scapes, and papillate heads, 

 it gives 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 64*^"^, yet single mats frequently cover 

 16^^'", averaging about 1000 plants to the square meter. Propaga- 

 tion is by stolons and migration is centrifugal, with a slow but positive 

 occupation. Mats unite and take complete possession of extensive 

 plats, yet it yields before Poa praiensis, in no way being able to 

 hold its own against this sod-forming mesophyte. 



The prevernal floral aspect of the formation is terminated by the 

 appearance of Ranunculus ovalis, Astragalus crassicarpus, and Draha 

 micrantha toward the end of the third week of April. They appear 

 in bloom almost simultaneously, but in no way contribute equally to 

 the aspect. Draba occurs only where the soil is exposed and the 

 grass is bunched, hence on upper xerophytic slopes, and appears to be 

 forced out whenever a close association is formed. It is an annual 

 of marked xerophytic tendencies, its leaves being basal and heavily 



