



of Mississippi and Louisiana 81 



leguminous plants. Here, too, the willows become more numer- 

 ous and the cypress comes in. 



Ballast 



At the lower end of the south pass there occur a number of 

 plants which are adventive from many parts of the world. These 

 have been brought in ballast which has been dumped along the 

 banks near Port Eads where these exotic forms are to be found in 

 considerable profusion. A few have already become established 

 and probably others will be established in the future. The ballast 

 plants are chiefly tropical and subtropical in their origin. 



Phvtogeography 



The general geographical relations of the Delta island flora 

 may now be indicated briefly. 



We notice with Kearney the infrequency of parasitic fungi, and 

 it seems probable that his explanation is correct, namely that the 

 adaptations which serve to inhibit transpiration enable plants to re- 

 sist the attacks of parasites. Other fungi are also scarce.. A very 

 few boleti and polypori were collected. 



The algal flora has already received mention. It may be added 

 that a certain species of green alga occurs in quantity on the sur- 

 face of the muck marshes, and attached to the lower parts of the 

 stems of Spartina and other muck marsh plants. Otherwise the 

 algal flora is very meagre. 



Lichens are abundant on the limbs of trees (oaks and mynca 

 and sometimes on the ground on the larger islands. 



) 



Mosses are rare excepting in a few favored localities on the 

 larger islands. 



Liverworts are rather more abundant but are not striking in 

 quantity or number of species. Some Lejeunea forms occur indi- 

 cating a general tropical character of the hepatic flora. 



Certain widely distributed ferns occur, and these will be men- 

 tioned in the list. They do not, however, form more than a weak 

 element in the plant covering of the larger islands. 



Regarding the spermatophyta we may make the following pro- 

 visional statements : 



I. Extended sand plains, removed from the direct influence of 



