THE DUNES AND THEIR PLANTS 



141 



new dune forms near 

 the shore it diverts 

 the strong winds in 

 its neighborhood, for 

 they are blocked in 

 certain directions and 

 go scurrying around 

 its ends to blow with 

 great vigor upon the 

 older dunes from new 

 angles. Not infre- 

 quently a poorly pro- 

 tected portion of some 

 old dune is exposed 

 thus to the scouring 

 action of the sand- 

 laden blast, and its 

 relatively loose soil 

 begins to blow away. 

 What was an estab- 

 lished dune may be 

 more or less com- 

 pletely blown away 

 (Fig. 14). Such blow- 

 outs are common, 

 and they, of course, 

 set back an area 

 that had perhaps 

 arrived at the 

 black oak stage to 

 the fore-dune stage 

 of shifting sands in 

 which only the few 

 hardy annuals can 

 grow. 



Fig. 138. — Yellow lady's-slipper, Cypripcdimn parvi- 

 florum. I. Front view of flower; 11, III, side and front 

 view of stigma and pollinia. Drawing by L. N. Johnson. 



