1908] HARVEY— PRAIRIE-GRASS FORMATION 97 



slopes and is found inclusive in Poa sods. C. festucacea occurs 

 likewise on lower slopes, but more abundantly and assumes the 

 " bunch-habit " of growth. Both the carices perennate and propagate 

 vegetatively by rhizomes. They contribute little if any to the floral 

 tone of the aspect. 



Florally associated with the carices, as just noted, are Vicia linearis, 

 Senecio plattensis, and Pentstemon gracilis, to which are soon added 

 Lapp ula texana and Plantago Pitrshii. Vicia occurs rarely, is confined 

 to lower slopes, and exerts no tone effect; it is a perennial form 

 and is pollinated by bees. Senecio, also of rare occurrence, seems to 

 be confined to mesophytic portions of the formation. It is conspicu- 

 ous on account of its numerous yellow heads and ray flowers. But 

 for its limited occurrence it might easily dominate the tone, and in 

 the vicinity of Sioux City it was recorded as controlling the aspect. 

 The achenes are provided with a copious pappus and a wide distribu- 

 tion is assured. It is a perennial, and its scarcity seems to indicate 

 that it is of decidedly mesophytic tendencies; it may be considered 

 prophetic in our area. Pentstemon gracilis, though rarely a com- 

 ponent in any plot, is an interesting form. It is confined to the 

 mesophytic portions of the prairie and has been noted as abundant 

 in western Iowa. Its rarity in our area is explained as in the case of 

 Senecio; it is a perennial, and its smooth though numerous seeds are 

 limited in their distribution. Lappula texana, the hairy stick-seed, 

 is also a minor element, occurring mainly on lower slopes in sparse 

 abundance. It is much branched and its numerous small blue 

 flowers exert but a restricted effect. It is an annual and very fertile, 

 producing numerous nutlets whose margins are each bordered by a 

 single row of bristles with recurved tips; distribution is entirely by 

 aid of animals. It continues to bloom well into the estival aspect. 

 The prairie plantain, P. Purshii, is a woolly annual whose indetermi- 

 nate spikes rise some 2o cm . Of copious abundance and of gregarious 

 habit, it frequently becomes conspicuous at short distances. Its 

 flowers bloom progressively up the spike, reaching the maximum in 

 the early estival aspect and continuing well into July. Its highly 

 immobile seeds prevent other than a limited distribution, thus readily 

 accounting for its gregarious habit. 



The fourth week of the aspect, about the last week in May, is 



