MARYLAND WEATHER SERVICE 1 i O 



mains. As the level rises, the line of shrubs and of trees advances 

 steadily toward the stream. 



Salt Marshes. 



The requisite for a salt marsh is a shallow body of salt or brack- 

 ish water which is not too much disturbed by littoral or fluvial 

 currents or by wave action. Hence these associations occur at the 

 mouths of streams and in embayments along a great part of the 

 coast line of the district under consideration, i. e., along Chesa- 

 peake Bay, the Potomac and the Patuxent rivers. Areas of this 

 kind were studied at Leonardtown, Chaptico and St. George's Island 

 in St. Mary's County, Parkers Creek and various places along the 

 Patuxent in Calvert County, West River and Patapsco River in 

 Anne Arundel County, Bush River and Gunpowder River in Har- 

 ford County. Since all the rivers of the region are tidal, the influ- 

 ence of the salt is felt for more or less distances up the rivers. Ac- 

 cordingly halophytic vegetation extends along the edges of the 

 streams to a distance which depends on the width and slope of the 

 channel and the distance from the mouth of the Bay. 



The vegetation of the salt marshes is altogether distinctive, for 

 only a limited number of species have adapted themselves to the 

 unusual conditions which here prevail, viz: (1) a relatively high 

 osmotic pressure of the water in the substratum, (2) a periodic 

 rise and fall in the level of the water, (3) a soft and unstable sub- 

 stratum, and frequently (4) the deposit of sediment coming by 

 means of river or shore currents. Among the plants which have 

 acquired the ability to live amid such conditions are preeminently 

 certain grasses of the genus Spartina, in which the following fea- 

 tures are noteworthy: (1) their extensive system of stout rhizomes 

 which securely hold the plant in the yielding substratum; (2) the 

 well-developed papery sheaths of the leaves, which prevent free 

 access of salt water; (3) the power of rolling up possessed by the 

 leaves, tending to enclose the stomata and so check transpiration. 



The last features and some others are shown in the photomi- 

 crographs on Plate XV of the leaf of Spartina stricta vai\ 

 maritima. Pig. 1 represents a transverse section from the central 



