Chap. I] 



THE FORMATIONS 



183 



In many other respects also, Spinifex squarrosus exhibits a close 

 connexion between structure and mode of life, for example in its leaves, 

 the waxy coating and structure of which express the difficulty in 

 obtaining water on the high permeable and salty dunes. Its spherical 

 infructescence, however, formed of stiff bristles and nearly as big as 

 one's head, claims special attention. When it is ripe, it breaks off from 

 its dry stalk and becomes the sport of the wind. Rolling and dancing, 

 it is hurried along the smooth surface of the sand and allows its fruits 

 to drop. The bristles are gradually worn away, and the infructescence, 



Fig. 98. Shore of Garden Island, Lake of the Woods, Minnesota. Salix fluviatilis predominant. 

 Besides this, Capnoides micranthum, Chenopodium album, Polygonum ramosissimum, and other 

 plants. From a photograph by MacMillan. 



now become cumbersome, is buried in the sand with the rest of the 

 fruits. 



Spinifex squarrosus, as regards its mode of growth, belongs to a very 

 widespread type. A peculiar type, on the other hand, is formed by 

 the species of Pandanus on the sandy sea-shores, which become firmly 

 anchored in the shifting sand by prop-roots that grow down from the 

 branches (Fig. 122). 



In many plants living on the sandy sea-shore, at all events particularly 

 in those that occupy sheltered spots, such obvious adaptations do not 



