1 84 



FORMATIONS AND GUILDS 



[Part II 



occur. Yet compared with other plants the}- have ahvays an extra- 

 ordinarily deep and extensive root-system. 



Sandy shore-formations, similar to those bj- the sea, are also found 

 by many saline or fresh-water inland lakes ; but there the dunes are 

 usually less pronounced in character, owing to the reduced strength of 

 the wind and the smaller amount of sand. The formations in question 

 have been described in much detail and in a very instructive manner 

 b}' Conway IMacMillan, as they occur about the Lake of the Woods, 



Fig. 99. Dunes on the lie aux Sables, Lake of the Woods, Minnesota. Populus tremuloides 

 Juniperus communis, and Prunus pumila in the foreground and to the left; Elymus canadensis am 

 Artemisia in the background. On the top of the dune, stunted little trees of Celtis occidentalis an 

 Cerasus pennsylvanica. From a photograph by MacMillan. 



a moderate-sized lake (about 1,500 square miles in area) situate between] 

 Minnesota and Canada. The banks are partly rocky, partly loamy 

 partly sandy, and partly covered with humus. Fig. 98 shows the sand) 

 flat shore, with a vegetation consisting chiefly of willows. Fig. 99 show; 

 low dunes grown over with various grasses and shrubs. 



Obviously the sandy shore of fresh-water lakes differs from that of tht 

 seaside, owing to its poverty in salt, and confers a xerophilous characte: 

 only on the vegetation of the higher dunes. 



