332 



THE IRIS VERSICOLOR ASSOCIATION 



With the draining- of the stations of Carex by the lowering of the 

 water-level, or otherwise, the hummocks are exposed. This is usu- 

 ally followed by a marked increase in the number of plants of Iris 

 versicolor and a reduction in the amount of Care.v. Grasses, es- 

 pecially Poa coiuprcssa and Poa pratensis, spread over the hummocks, 

 while Iris and the secondary plants for the most part occupy the 

 spaces between the hummocks. 



Most of the stations of this association are in the stage charac-. 

 terized above. A few in more advanced stages indicate that if the 

 water-table is further lowered, the Iris association will ultimately be 

 replaced either by grass or by the Liatris spicata prairie association, 

 iln other situations, especiahy near the foot of the bluff south of 

 Beach, where the ground is more boggy, the Iris occupies a tension 

 zone between the carices and the thickets, persisting as a relic in case 

 of succession by the latter association. It is very frequently present 

 as a transition zone between the swale associations and the ridge as- 

 sociations, between which there are usually no successions although 

 they may grow in direct contact with one another. 



The association is characterized by plants that prefer a somewhat 

 boggy soil which is always moist yet rarely inundated. The vegeta- 

 tion is very compact and invasion into it is rather slow. This associ- 

 ation presents conspicuous aspects during the different seasons. The 

 blooming- of the dominant species itself characterizes the spring as- 

 pect. During the summer the abundant yellow flowers of Steironema 

 qiiadriflormn again make this association conspicuous. Vervain ( Ver- 

 bena hastata), smartweed {Polygonum piinctatum), Solidago gramini- 

 folia, and boneset (Bnpaforiuin perfoliafinn) combine to produce the 

 serotional aspect, while several species, most important of which are 

 ladies' tresses (Spiranthes cernua), closed gentian {Gentiana an- 

 drewsii), Gerardia paiipercida, Gerardia tennifolia, and a few asters, 

 make up the fall aspect. Very small, single-flowered plants of Gen- 

 tiana pro c era continue blooming late in the fall, until finally killed by 

 the severe frosts towards the end of October. 



LIST OE THE SPECIES OE THE IRIS VERSICOLOR ASSOCIATION 



Dominant Species 

 Iris versicolor Blcocharis iufenncdia 



Secondary species which are most abundant 

 Lye opus americanus Verbena hastata 



Steironema quad rid orimi Prunella vulgaris 



