101 



The snccessional relation between the Paniciun psendopuhescens 

 and the windward slope associations is self-evident, since there is an 

 actual transfer of individuals from the former to the latter. The 

 basin is developed directly within the Panicum pseudopnhescens asso- 

 ciation by a mere chang-e in the nature of the sand movement, and 

 also represents a direct succession. Because of the environmental 

 conditions there are seldom any relics which survive. The succession 

 represents a case where the preceding vegetation is entirely destroyed 

 before the next stage appears. The deposit association also succeeds 

 the Paniciiiu pscndopnhesceus association directly and relics frequently 

 occur. On the lee slope the movement of the sand is similar to that 

 going on in the intervals between the bunch-grasses, so that the 

 blowsand may be regarded as another direct succession. All four 

 associations of a typical blowout, therefore, may and do arise simul- 

 taneously and independently. 



The general appearance of a typical young blowout is shown in 

 Plate VI, Fig. i. The total width of the blowout from west (left) to 

 east (right) is about 20 feet (6 m.). At the left is the edge of the 

 Panicum pseudopnhescens association, with many relic bunches of 

 Andropogon scoparius and in the extreme left foreground a bunch 

 of Carex MiMenbergii. From this will develop the windward slope 

 association. Along the right is a conspicuous zone of Panicum 

 znrgatnm, marking the deposit association, with relic bunches of 

 Panicum pseudopuhescens and Carex nmhellata. The central basin 

 is still bare and the lee slope is scarcely differentiated. A transect 

 across this blowout is given in Table III. 



Table III Transect ok 20 quadrats, each 5 dm. square, across the 



BLOWOUT SHOWN IN PL- VI, FiG. 1. 



I^inaria canadensis XX XX---------------- 



Paniciim pseudopubescens XXXX------------X--- 



Andropogon scoparius X-- .----..-- 



Bouteloua hirsuta .X------------------ 



Festuca octoflora -X---- 



Carex Muhlenberg-ii ..X-------- X-- 



Carex umbellata ----XX-X -XX--- 



L/espedeza capitata ------X - 



Croton g-landulosus --- ---X---------X--- 



Aristida tuberculosa ...-.--_ X------ 



Ambro-ia psilostachya ...--.--_------X---- 



Panicum virgatum --...----------XXXXX 



Equisetum laevigatum -- --------X-X 



Koeleria cristata ..-.-.- -X-- 



