VEGETATION OF DUNES AND SANDY HAMMOCKS. 131 



The slender, wiry culms of this grass, 3 to 4 feet high, with scanty 

 involute rigid leaves, when bending under the burden of the large, 

 more or less contracted, panicles of the broad, many-flowered 

 drooping spikelets, render the species one of the most strik- 

 ing types of psammophile plants. It inhabits the dunes from the 

 southern frontier of Virginia through North Carolina south to Texas 

 and the Mexican coast. By its stout running rhizome, deeply buried 

 in the sand and sprouting from the rather distant nodes, a single 

 plant soon colonizes the bare dune. The flowers appear to be mostly 

 infertile, as no spikelets with well-matured grain have been observed 

 in the specimens from our coast. Ipomoea carnosa, similar in its sub- 

 terranean stems and root system to the above grass, is not infrequently 

 found along with it, the numerous long prostrate stems bearing bright- 

 green leaves, which cover the sand. Opuntia crus-corvi and Siphony- 

 chia erecta are not rare in the same localities. The dead tops and 

 branches of the sand pine (Pinus clausa] and tops of the Spanish dag- 

 ger (Yucca aloifolia], with the trunks almost completely buried in 

 the drifting sands, increase the impression of aridity on these desolate 

 shores. 



Mesophile plant associations of the dunes. In the shallow sandy pools, 

 formed mostly by the accumulations of rain water in the depressions 

 and rendered more or less brackish by the influx of the waves of the 

 sea during storm tides, many of the plants of the semiswampy coast 

 plain mingle with types of various families not found outside of the 

 littoral belt. Of the former class occur the following, the first two 

 being most frequent: 



Rynchospora torreyana. lAnum medium. 



Hypericum aspalathoides. Scleria pauciflora glabra. 



Lechea torreyi. 



Of plants peculiar to the littoral belt occur: 



Sdrpus americanus. Xyris torta pallescens. 



Fuirena scirpoidea. Cassia (Chamaecrista) mississippiensis. 



Scleria gracilis. 



Open groves of Cuban pines cover the flats behind the dunes, merg- 

 ing frequently into the pine meadows of the coast plain. 



Xerophtte plant associations of the sandy dry hammocks. Between 

 Bon Secour and Perdido Bay low, sandy hills or ancient dunes, rising 

 above the saline swamps, support a high forest of evergeen trees, 

 principally live oak, but with a mixture of laurel oak and Cuban and 

 long-leaf pine. On these dry, sandy hammocks the sand pine (Pinus 

 clausa), frequent in peninsular and western Florida, reaches its western 

 limit. In this locality the tree has been found from 50 to 60 feet high, 

 rarely over a foot in diameter, breast high. Stunted Spanish oak, 

 barren oak, blue jack, and the common wax myrtle form the under- 

 growth, and the procumbent stems of the saw palmetto deeply rooting 



