132 THE PLANT LIFE OF MARYLAND 



FRESH MARSHES. 



The areas of Fresh Marshes which have been examined on the 

 longer rivers of the lower Chesapeake Bay exhibit a close agreement 

 on the Pocomoke River opposite Rehoboth, on the jSTanticoke at 

 Vienna and on the Choptank in the vicinity of Dover Bridge. The 

 spring aspect of the Marshes is monotonous, and the summer months 

 are the period of greatest vegetative activity. It is only in Septem- 

 ber that one may gain an adequate idea of the richness of the flora, 

 and from then until frost the marshes are conspicuously beautiful, 

 the varied shades of green being softened to rich browns, and 

 brightened by the yellow and purple flowers of Bidcns and Vernonia. 



The extreme outer margin of the marshes is formed by Nymphaea 

 advena, and adjacent to it is a zone in which are also such emersed 

 aquatics as Peltandra virginica, Pontederia cordata, Sagittdria 

 latifolia and Scirpus lacustris. In this outermost zone Hibiscus 

 moscheutos sometimes occurs in great abundance, or in a few places 

 where there are natural dykes along the outer edge of the marsh 

 and along one side of the streamways through it, Baccharis lialimi- 

 folia may be found, as on the ISTanticoke about four miles south of 

 Vienna. 



The one fresh water plant which is more capable than any other 

 of resisting brackish conditions is Scirpus americanus. Only slightly 

 less so are Scirpus olneyi, Scirpus robustus, Spartina polystachya 

 and Zizania aqualica. These species are the first that are encount- 

 ered in passing up stream out of the purely halophytic marshes, and 

 Spartina stricta var. maritima and Spartina patens soon give way 

 to stands in which one or another of these is dominant, for they are 

 never associated in a uniform admixture over areas of any extent. 

 There are no observable differences in physical conditions to ac- 

 count for the sporadic occurrence and distribution of the stands of 

 these several plants, which appear to be ecologically equivalent and 

 to dominate or give way according to the chance conditions of repro- 

 duction by either seeds or rootstocks. The only other species which 

 form pure stands with any frequency are Phragmites phragmites, 

 which is however, not at all a common grass in the marshes, al- 

 though it is confined to them in its occurrence in Maryland, and 



