294 



tion there is very little difference ecologically between this area and the 

 middle beach. The habitat is dissophytic, because the underground 

 parts of the plants are in mesophytic to hydrophytic condition accord- 

 ing to the water content of the soil, while the upper parts are sub- 

 jected to rather severe xerophytism. The desiccating effect of the 

 wind and sun are met by adjustments in the plant structure (cf. 

 Kearny 1 900 :276-28o ) . 



The Association.' — The association is an open one, in which about 

 30 to 40 per cent, of the area is vegetated. From 30 to 50 per cent, 

 of the vegetation is occupied by the dominant species, wormwood 

 {Artemisia candata), which gives a grayish tone to the soil. Cowles 

 (1899:168) says that the most characteristic plants are Artemisia 

 candata and A. canadensis. In the Beach region, only the A. candata 

 is present. In a similar area near Rogers Park, Chicago, a few miles 

 south, both species occur. Another dominant species, Panicnm vir- 

 gatum, which Jennings found at Cedar Point and Presque Isle, is of 

 relatively little importance in this association in this region, although 

 it occurs not infrequently. Its place is taken by Sporoholus cryptan- 

 drus, which grows in clumps somewhat like a bunch-grass. Its 

 growth habit is illustrated by Figure i, Plate L. This plant, how- 

 ever, is usually more characteristic of blowouts. 



These three character species occupy about 95 per cent, of this 

 area in typical situations of this association. Typical examples are, 

 however, rather rare in this area. The best developed of them is 

 about a kilometer north of the Lake County pest-house. There, this 

 association is eight to ten meters in width and approximately twenty 

 meters in length. Usually the invader, Andropogon scoparius, gives 

 a decided character to the appearance of this association, in which it 

 groW'S at intervals of two to three meters. 



Of the other species which Cowles has listed as characteristic of 

 this association, only four specmiens of Pitcher's thistle (Cirsium 

 pitcheri) have been found. A very few plants of beach pea {Lathy- 

 rus maritimns) occur here, although it is commoner on the lee slopes 

 of the Amuiophila dunes. A spurge (Buphorbia polygonifolia) is 

 fairly abundant, although it can not be so characteristic as on the 

 middle beach. Evening primrose, Oenothera biennis, does not occur 

 in this association, and a grass (Agropyron dasystacJiyiim) does not 

 grow in the region. 



Secondary species occur more or less throughout the association, 

 but are most abundant near to the margins, where the prairie element 

 has commenced to invade. They are not usually numerous, but fre- 

 quently, because of their bright-colored flowers, seem to be nearly 



