264 



BOTANICAL GAZETTE 



OCTOBER 



from the edge of a blowout. The conditions are very similar at 

 A and B so far as the humus is concerned. This has attained a 

 thickness of approximately 5 cm., which is indicative of a rela- 

 tively long period of stability. The presence of a well denned 

 humus is correlated with a very rich development of herbaceous 

 undergrowth and tree seedlings. 









Fig. 2 



Fig. 3 



Figs. 2, 3. — Fig. 2, station B, showing position of Tilia at base of well established 

 dune and with same plant associates; fig. 3, station C, where Tilia is located on 

 edge of blowout; humus being broken up by sand movement, and access of wind 

 and light much greater than at A or B. 



Station C (fig. 3) is located on a west-facing slope on the edge 

 of a blowout where there is a ready access to strong winds. The 

 exposure to light is much greater here than at either A or B, 

 especially in the afternoon when the sun's rays fall vertically upon 

 the slope, while the stations in the forested complex are deeply 

 shaded. The free sand movement has destroyed the humus and 



