206 EDWARD B. COUCH 



the first three quadrats and dominant in the fourth it seems to 

 rank second to Gaertneria as a sand binding plant. 



In the fourth quadrat Ahronia umbellata is the dominant plant 

 with Eriogonum and Lupinus as secondaries. Gaertneria has lost 

 its place and become a relict perhaps of former formations or is 

 of accidental occurrence. 



Quadrat number five shows Adenostoma as dominant and 

 Ahronia umbellata and Cherianthus as secondaries. Adenostoma 

 appears suddenly and in so doing rather upsets the series of 

 dominants and secondaries. It however is peculiar to the sum- 

 mit and leeward slope and occurs just as markedly as the quadrat 

 count indicates. It does not occur on the windward slope. It is 

 possible that Eriogonmn should also be named as a secondary in 

 this quadrat. 



Quadrat six gives Cherianthus as dominant by numbers and 

 Adenostoma and Eriogonum as secondaries. The size of the plants 

 however place them in reverse order. 



In quadrat seven the most conspicuous plant of the dunes in 

 dominance is Lupinus. The land is so nearly occupied that to 

 name a secondary would be stretching the meaning to apply to 

 mere numbers. 



The two kinds of competition exist, that between plants and 

 their environment and that between plants themselves. In gen- 

 eral the competition on the windward slope is environmental that 

 of the summit a combination of environmental and vegetative 

 and that of the leeward slope mainly vegetative. In both cases 

 where the competition is greatest the number of species is the least. 

 In case of environmental competition the plants do not cover the 

 surface of the soil, but in the case of vegetative competition the 

 surface is covered in proportion as the competition is close. In 

 other words, open formation occurs on the windward slope and 

 slightly so on the summit, while closed formations are the rule 

 on the leeward slope and at the foot of the dune on that side. 

 Gaertneria and Ahronia umbellata seem to be the most successful 

 in the environmental competition and Lupinus in plant compe- 

 tition. The regions giving greatest number of species in the 



