348 THE ALGAE 



Strangford Lough in Ireland and at Aberlady near 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 

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

 bedded 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 inter- 

 mediate 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 volubiHs, caespitosus 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 fiUformis. 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 female. 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 is a free-Hving 



