186 THE PLANT LIFE OF MARYLAND 



Although not of the same extent as those on the Atlantic coast, 

 typical instances of strand associations occur at numerous places 

 along the Chesapeake and Potomac, as at Rock Point, Charles 

 County, Piney Point, St. Mary's County, Bay Ridge, Anne Arun- 

 del County and Chesapeake Beach, Calvert County. In these de- 

 cidedly xorophytic situations plants are not numerous in either spe- 

 cies or individuals, and show many adaptations to the severe condi- 

 tions, a full account of which may be found in Kearney's Dismal 

 Swamp paper. Usually a distinct zonation may be observed, for 

 the conditions differ considerably at different distances from the 

 shore. 



The outer beach is usually devoid of vegetation. Algae cannot 

 gain a foothold in the space between tides on account of the shifting 

 nature of the sandy bottom, while the area just above high tide is 

 exposed to alternate washing by waves and drying by the sun. 



Zone 1. — The middle beach. Beyond the reach of the waves of 

 summer though not those of winter are a few annuals whose tap 

 roots enable them to gain a footing, and which can endure a certain 

 amount of salt. Among these Cakile edentula with its fleshy leaves 

 and rocket-like fruits is widely distributed but not numerous in 

 individuals; Salsola kali also a fleshy-leaved plant, is more com- 

 mon ; Euphorbia poly goni folia owes its persistence to its prostrate 

 habit as well as to its relatively long tap-root. Besides these outliers, 

 specimens of the conspicuous yellow horned poppy, Glaucium glau- 

 cium, were collected at Piney Point, Solomons, etc. 



Zone 2. — Behind the area exposed to winter waves is one in which 

 a few perennials as well as annuals are able to establish themselves. 

 Grasses such as Spartina patens and Ammophila arenaria form small 

 clumps, while Capriola dactylon, — one of the few introduced plants 

 found on the strand, — sometimes occupies rather large areas. Its 

 habit of creeping and taking root at the nodes, together with its 

 power of withstanding drought, eminently fit it for capturing such 

 an area. Another grass of this zone, fortunately not occurring in 

 extended groups, is Cenchrus tribuloides. Plants of prostrate or 



