74 Lloyd and Tracy: The insular Flora 



the trees, on the slope of the mound Op 



Itifli 



& 



Breiveria, forming, however, a scanty plant covering only. Atten- 

 tion should be drawn to the fact that the epiphytic plants {Poly po- 

 dium polypodioides and Tillandsia us ?k aides) which are so common 

 on the live-oaks of the nearby mainland, are here entirely absent. 



Sand Dune Formation 



In addition to the dunes already described in connection with 

 the sand beach and sand plain formations there are two other dune 

 types which still remain to be mentioned. These are the estab- 

 lished dunes of low stature and the high wandering dunes. 



The former occur notably on Breton Island, and are usually 

 less than one meter in height. They are clothed with a thicket of 

 Ilex vomitoria and Myriea Gale, and with these is an undergrowth 

 of herbaceous plants such as have been referred to in the descrip- 

 tion of the open grassy sand plain, of which in point of fact, this 

 Ilex- Myriea dune formation is a part which has changed its aspect 

 as a consequence of the growth of those evergreens. The cause 

 of this change is obscure, but it seems probable that the shrubs 

 have been better able to establish themselves on the lee of the 

 grass plain. The formation corresponds very closely to the 

 thicket formation of Ocracoke described by Kearney, but lacks 

 the particular species mentioned by him. Owing to the rather 

 heavy protective covering of shrubby vegetation these low dunes 

 are not affected by the wind to an appreciable extent and may 

 therefore be regarded as in a relatively static condition, or other- 

 wise expressed, as established. 



Only one of the islands visited affords conditions favorable for 

 the formation of the high, wandering dunes, namely Cat Island, 

 where they are to be found on the windward side. They are ar- 

 ranged in a linear system which lies parallel with the shore line. 

 and range in height from ten to twenty meters. The most north- 

 erly dune of the system is the highest, and constitutes on this 

 account a prominent landmark. It is quite naked save on the 



lee 



Jatropa 



sp. and some others, gain a temporary foothold in the shade of the 

 trees which are doomed to partial or complete burial. The only rt 



