80 Lloyd and Tracy: The insular Flora 



elsewhere covered many acres. Tamariscinas and other Amaran- 

 thaceae are much more abundant here than on the sand islands. 

 Baccharis halimifolia is abundant on all the mud lumps and is 

 often the only woody plant. 



The Delta 



No attempt has been made in the preceding pages to include a 

 treatment of the phytogeographical conditions of the land of the 

 Delta, since it is a part of a region which justly requires a separate 

 study. The general statements pertaining to the more recent part 

 of that area are as follows. 



The " passes " of the Mississippi River are broad channels of 

 fresh water separated from the waters of the Gulf by an irregular 

 and frequently very narrow strip of land of river deposit. The 

 greatest elevation of the surface above sea level is on the bank of 

 and near to the stream. On the other side the land slopes grad- 

 ually away toward salt water, while toward the fresh water the 

 slope is abrupt. 



Two associations are to be recognized, both of which have 

 grasses as the determining elements. These are the Phragmites, 

 Vigna and the Spartina associations. The former occupies the 

 higher levels and therefore the portion of the bank near the fresh 

 water. The grass makes a dense growth, and spreads by means 

 of the long decumbent stems and stolons. These and the roots 

 bind the soil, which however is gradually eroded, leaving project- 

 ing clumps of the grass along the banks. From these clumps the 

 decumbent or prostrate stems project out into the water and sway 

 in the current, extending down stream 30 meters or more. On 

 the highest part of the bank the « canes " form a mechanical sup- 

 port for a very profuse growth of Vigna glabra which is almost 

 impenetrable. Occasional trees of Salix nigra and vines of Am- 

 pelopsis arborea are to be seen along the bank. 



In the swampy ground of the lower levels which border on 

 the salt water Spartina gives the character to the vegetation, and 

 this is often the sole plant. The two associations fade into each 

 other, but there is nevertheless a fairly distinct line of demarkation. 

 As one advances northward and as the land broadens out, a sort 

 of swamp meadow land is found, where occur many grasses and 



