271 



plants that occur, always at very widely separated intervals, are sea- 

 side spurge {Bnphorhia polygonifolia), cocklebur {Xanthinui com- 

 mune), and sea rocket {Cakilc cdentula), in abundance as named. 

 Each of these plants has to contend with a continual exposure of its 

 root system by the removal of sand. Buphorhia polyyonifolia usually 

 escapes this by living in depressions. If growing on the level, how- 

 ever, it forms a dense mat which holds the sand within its compass, 

 building up a miniature dune about two centimeters in hight and 

 sometimes twenty centimeters in diameter. (See Plate XLV, Fig- 

 ure I.) If the blowing is too vigorous, the plants will succumb, 

 and it is not unusual to find dead, curled-up plants of this species 

 rolling about in the wind. There is apparently no adaptation in 

 Cakilc for the protection of its root system, but XaiitJiiuiii is adapted 

 by growing procumbent with only the apical four to seven centimeters 

 projecting into the air. The spread of leaves around the stem aids 

 in the formation of a small, temporary dune which protects the root 

 system from exposure. Even then plants liave been found in which 

 there was a distance of 6- to cm. from the exposed bur, from which 

 the plant had germinated, to the point at which the root was covered 

 with sand. This indicates that considerable sand had been removed. 



Pieces of driftwood on the beach are often the starting points for 

 small, temporary dunes. Occasionally a plant of Xanthiuin commune 

 will fix such a dune for a season. In the vicinity of Beach, where 

 the middle beach is very narrow and protected by the fringing dune, 

 the characteristic plant is Buphorhia polygonifolia. This plant is 

 most abundant where there are pebbles to afford it protection from 

 the wind. Cakile edentula occurs only at rare intervals, while Xan- 

 tJiium is virtually absent. 



During the season of 1910, which was characterized by the ex- 

 treme duration of a protracted drought, the water-level of Lake 

 Michigan was very noticeably lowered. This made the wave action 

 on the ground occupied by this association virtually nil. In addition 

 to a normal abundance of the usual dominant species, there were 

 the following secondary plants, whose growing habits were soiue\yha,t 

 similar to those of the dominant species: Cycloloma afriplicifoliuui, 

 Russian thistle (Salsola kali fenuifolia) ; bug-seed (Corispcrmum 

 hyssopifoliuni), cottonw^ood {Popidus .dcltoides), and Sali.v syrficola. 

 AH of these plants were characterized by the extreme length of their 

 secondary roots. These spread radially from the small bushy plants, 

 giving the plani command of the water supply from an area eight to 

 fourteen feet in diameter. The roots were quite strong and could be 

 easily pulled up in lengths uf four to six feet. The plants themselves 



