Chap. I] 



THE FORMATIONS 



i8j 



North Sea. Behind the sandy shore, here rich in lime, there rises first 

 a range of dunes poor in plants, behind which there are dunes that are 

 better clad and which serve as a transition to the mainland. Only the 

 flat shore and the dunes lying nearest the sea exhibit in their vegetation 

 the characteristic influence of the habitat. Difficulty in fixing themselves 

 to the loose substratum, difficulty in obtaining a supply of water, a 

 struggle against the sea-wind, the use of the wind for the transport of 

 fruits on the smooth sandy surface, all these may at once be inferred 

 from the remarkable forms that occur. 



Fig. 96. Nebraska. Sandy deposits with open mixed formation of plants in a river-bed. In the 

 background, grassland formation (prairie") corresponding to the climate, and bare rocks. Photograph 

 from the Geological Department of Nebraska University. 



Adaptations in relation to such conditions are combined in the 

 clearest manner in Spinifex squarrosus, a rigid bluish grass, with large 

 globular inflorescences and infructescences T , which latter appear to be 

 composed of long radially arranged needles, the very long bracts. 

 Frequently Spinifex alone covers the outermost dunes bounding the Indian 

 Ocean with numerous apparently independent tufts ; a closer inspection 

 shows that, in many cases, even widely separated tufts are united by 

 stolons more or less imbedded in sand, varying in thickness from that 



1 See Fig. 369 for an illustration of the quite similar infructescence of Spinifex 

 hirsutus. 



