324 ECOLOGY OF SALT MARSHES 



the Firth of Forth but with no apparent intermediate stations. The 

 normal form is present in other areas where there are marshes in the 

 vicinity, e.g. the west coast marshes, but the marsh form does not 

 appear to have developed. The evidence at present available would 

 suggest that it has originated independently in the three areas, and 

 in that case it can only be concluded that certain conditions must be 

 fulfilled before the marsh form can develop from the normal 

 species. This is a problem that is still awaiting solution. 



One of the more interesting features of the algal vegetation of 

 salt marshes is the occurrence of the marsh fucoids. These are 

 peculiar forms which are either free-living on the marsh or else 

 embedded in the mud, and they must all at one time have been 

 derived from the normal attached form. Sometimes they bear a 

 fairly close resemblance to the attached form but in other cases 

 they have been very considerably modified, and it is only the 

 existence of intermediate forms which enables us to indicate the 

 normal type from which they came. East Anglia is essentially the 

 home of the marsh fucoids, although Strangford Lough in Ireland is 

 also extremely rich. In Norfolk, for example, considerable areas 

 can be found occupied by Pelvetia canaliculata ecad libera, whilst 

 the three marsh forms of Fucus vesiculosus, ecads volubilis, caespito- 

 sus and muscoides are also abundant, the last two being embedded in 

 the soil. 



Apart from these forms there are three other loose-lying marsh 

 forms derived from Fucus vesiculosus but these are confined to the 

 Baltic, e.g. ecads nanus, suhecostatus and filiformis. A small 

 crawling marsh form derived from F. ceranoides has been described 

 from the Irish and Dovey marshes, and another larger free-living 

 one from Strangford Lough in Ireland; like many others of this 

 type it is profusely branched, fertile conceptacles are rare and, when 

 present, are invariably male. F. spiralis vars. nanus and lutarius are 

 other marsh derivatives, whilst Pelvetia canaliculata not only gives 

 rise to ecad libera but also to a small embedded form, ecad radicans, 

 which has been recorded from the Dovey marshes. There is also 

 another form, ecad coralloides, which has been described from 

 Blakeney and more recently from the Cumbrae marshes, but until 

 more is known about this particular ecological form it ought to be 

 regarded with some degree of caution. Ascophyllum nodosum var. 

 minor is a dwarf embedded variety, ecad Mackaii of the same species 



