106 



a stabilized area behind the active basin, following- it as it moves 

 forward. 



The flat open deposits without efficient dune-formers are stabil- 

 ized in nearly the same way. Paspahnn setaccum first becomes more 

 abundant and is followed by large numbers of Sporoholus cryptan- 

 dnts, with the usual g-rowth of Lcspcdcza and Oenothera. Follow- 

 ing- these the bunch-grasses appear. A tract in the Oquawka area 

 shows the results of twelve years of stabilization in this w^ay. The 

 field w'as formerly blowing actively, until some locust trees were 

 planted as a windbreak at the west side. In the twelve years that 

 have elapsed most of the blowouts have Ijecome extinct and the 

 extensive flat deposits have been almost entirely stabilized. Oeno- 

 thera rhonibipetala and Leptoloina coi:^natinn constitute the dominant 

 species at the present time. The launches of the latter are round and 

 compact, but widely separate, and cover only about 30 per cent, of the 

 ground. Oenothera is so abundant that when in bloom it shows 

 almost a solid mass of color. But nine accessory species have 

 appeared: Paspahnn setaccum, Ambrosia psilostacJiya, Boutcloua 

 Jiirsiita, Crofon glanduJosus, var. septentrionaUs, Cyperus Schivcinit- 

 zii, Lcpidiiini virginicum, Monarda punctata, J^erbena stricta, and 

 Physalis virginiana. Proceeding up the lee slope from a partially 

 active blowout toward this newly developed bunch-grass, the grasses 

 appear in the following sequence : Paspalum, Sporobolus, Leptoloma. 

 In this case the horizontal arrangement probalily indicates the suc- 

 cesion in time as well. 



THE HUDSONIA ASSOCIATION 



In the Hanover area blowouts are sometimes stabilized by Hnd- 

 sonia tomcntosa, which fonns a peculiar association of its OW'U. 

 Hiidsonia grows in dense hemispherical tufts up to 4 dm. in diam- 

 eter and is always gregarious, occupying 10 to 50 per cent, of the 

 whole surface. It can not endure burying and does not possess the 

 power of growing up with the deposition of sand. Consequently 

 it does not live on deposits. Similarly it can not well resist under- 

 mining and does not live in basins or on windward slopes. Neither 

 has it been observed on actively moving- lee slopes, nor is it able 

 to hold its own in competition with 1)unch-grass. Its optimum 

 habitat seems to l:»e open quiet sand, and it is restricted therefore to 

 young l)lowouts in which the surface is nearly flat and the sand is 

 not actively in motion, or to small portions of more active blowouts 

 where it is al)le to get a foothold. The plants appear first at the 



