330 



abundant production of seeds in a dry season is a xerophytic adap- 

 tation. 



The Cladium association may be displaced by a thicket, but in 

 nearly every case it is succeeded by the blazing star (Liatris spicata) 

 prairie. This latter succession tal<es place more easily when the Cla- 

 dium is not restricted to a narrow belt. The species that invades first 

 are usually Lyihruiii alatuin, Solidago grmninifolia, Pycnantheinuui 

 virginiamnn, Oxypolis rigidior, Gerardia paupercida, Bpilohiimi den- 

 sum, and Liatris spicata. 



LIST OF THE SPECIES OE THE CLADIUM MARISCOIDES ASSOCIATION 



Dominant Species 

 Cladium ni arise oidcs 



Secondary Species 

 Hypericum virginianum (scarce) Spavtina michauxiana (scarce) 



Relic Species 

 Briophorum augustifolium Utricularia cornuta 



Scirpns americanus Aspidium thelypfcris 



Invading species, nowhere abundant in this association 

 Lythnim alatmn Bupatorium perfoUatum 



Solidago graminifolia Steironema quadritlorum 



Pycnanthemiim lirginianum Liatris spicata 



Oxypolis rigidior Lycopus americanus 



Gerardia paupcrcula Lycopus sp. ? 



Bpilobium densum Osuiunda regalis 



Potentilla fruticosa Iris versicolor (uncommon) 



Solidago ohioensis Habenaria psycodes (two individ- 



uals) 



THE CALAMAGROSTIS CANADENSIS ASSOCIATION 



When swales have reached a sufficiently advanced stage of de- 

 velopment, Calamagrostis canadensis appears on the tension line 

 between the Cladium and Scirpus americanus associations and ulti- 

 mately entirely replaces the Cladium. The Calamagrostis associa- 

 tion occupies somewhat mucky soil in which, a little above standing 

 water but not sufficiently high for the surface to become dry, an 

 abundance of Marchantia polymorpha may occasionally be found. 

 It is not usually subject to inundation. From 98 to 99 per cent, of 

 the area of this association is occupied by the marsh grass, Calam&- 



