1908I HARVEY— PRAIRIE-GRASS FORMATION 99 



few days of June. Gaura coccinea, Meriolix serrulata, Psoralea 

 esculenta, Hedeoma hispida, and Osmodium molle now progressively 

 appear. Though flowering during the transition from vernal to 

 estival aspect, these forms reach their maximum display during the 

 early estival; particularly is this true of Meriolix, Hedeoma, and 

 Osmodium. They should be considered transitional species, which 

 appear during the unsettled climatological conditions between the 

 vernal and estival periods, and are not specially indicative of either. 

 Of subcopious occurrence and largely overtopped by leafy stalks of 

 autumnal forms they must be ranked as almost neutral in the floral 

 aspect. Gaura coccinea is a relict of more xerophytic stages and occurs 

 primarily though sparsely in the open association of upper slopes 

 and crests. It is an annual and a low and obscure element. It 

 bears a few-seeded iridehiscent nut of little mobility. Meriolix may 

 also be considered as a relict of the xerophytic stages of the prairie, 

 having its present distribution limited to the open association along 

 crests and upper slopes, where it frequently occurs subcopiously. 

 Its large yellow flowers make it conspicuous, but only at short range, 

 as low stature relegates it to a sublayer. It is a slightly shrubby 

 perennial from a woody root, producing numerous seeds which are 

 strikingly immobile. It continues blooming up into the autumnal 

 floral aspect, but reaches its maximum in the early estival. Psoralea 

 is rare and of solitary occurrence on middle slopes; add to this its 

 inconspicuous fading-blue flowers and it is scarcely seen upon the 

 prairie by the casual observer. It is a perennial from a large edible 

 farinaceous tuberous root. In the autumnal aspect, breaking off 

 close to the ground, it becomes a tumble-weed. Its rarity is prob- 

 lematical. Hedeoma, a low annual, scarcely ever more than zO^^ 

 high, occurs subcopiously and not infrequently copiously upon 

 middle slopes. Its low stature and leafy branches completely 

 hide its abundant small blue flowers, rendering it ever incon- 

 spicuous. Osmodium occurs sparsely though quite generally over 

 the whole formation, with the exception of the very crests. It is 

 a perennial with several stalks, terminated by leafy, pendent, scor- 

 pioid racemes of greenish flowers, arising from a thick root. It 

 is also quite unnoticeable. The smooth nutlets possess limited 

 mobility. 



