MARYLAND WEATHEB SERVICE 181 



for by seepage from the banks, or by the presence of a bar separating 

 this part of the marsh from tide-water. In the latter case a prac- 

 tically fresh marsh may exist very near salt water as may be ob- 

 served at Cove Point on Chesapeake Bay. As the area becomes 

 drier it is invaded by a variety of dicotyledonous plants, conspicuous 

 among which are the two malvaeeous species Hibiscus moscheutos 

 and Kosteletzhya virginica. In a marsh of this kind on Bush River 

 Neck, Harford County, it was observed that the Gerardia maritima 

 of the marshes farther down the Bay was replaced by Gerardia 

 purpurea, and Sabbatia stellaris was replaced by Sabbatia dode- 

 candra. 



Juncus roemerianus occurs in considerable masses in several 

 places, e. g. on St. Georges Island, southern St. Mary's Comity 

 (also at Ocean City), but hardly warrants being placed as a distinct 

 association, though Kearney (op. cit.) found it abundant in the 

 Dismal Swamp region. Spartina patens also forms somewhal ex- 

 tensive mat-like groups in a similar habitat to and mixed with 

 Distichlis, as was observed on Fishing Creek, Calvert County; it 

 also oeciirs in a somewhat different habitat, namely, on the strand, 

 where it usually grows taller. This larger plant is by some consid- 

 ered a distinct species, — Spartina juncea. Another plant found in 

 very dry situations and also on the border of tidal streams is 

 Strophostyles umbellate*. 



It may be gathered from the foregoing that the distribution of 

 these associations depends: (1) on the amount of salt in the sub- 

 stratum, (2) on the water-content of the substratum. Hence a 

 zonation may be observed (1) as one proceeds up a tidal stream. 

 and (2) in the direction of the bank. In the latter case a distinct 

 zonation occurs only when the formation of the marsh has been 

 uniform and gradual. The zones are arranged as follows, though 

 in no one place are all of them likely to be present: 



I. Spartina stricta association 



or Spartina polystachya assoc. 1 Marginal zones de- 



or Scirpus olneyi association I termined by salt Con- 



or Typha association tent etc. 



II. Scirpus olneyi association 



