ECOLOGY OF SALT MARSHES 349 



form found on American salt marshes, in Scotland and on the 

 shores of Strangford Lough in Ireland, whilst ecad scorpioides is a 

 partially embedded form found on the Essex marshes, on the 

 shores of Strangford Lough and in eastern North America. All 

 these forms probably originated as a result of vegetative budding, 

 although it is also possible that they have developed from fertilized 

 oogonia that became attached to phanerogams on the marsh. There 

 is definite evidence that Ascophyllum nodosum ecad scorpioides arises 

 by vegetative budding from fragments of the normal plant, whilst 

 it has been suggested that conditions of darkness or lowered salinity 

 may be favourable for the development of ecad mackaii (Gibb, 



1957)- ^ ^ . 



Although there are no species of Fucus in the southern hemi- 

 sphere, an interesting free-living form of the southern fucoid 

 Hormosira banksii has been recorded from mangrove swamps in 

 New Zealand. It does not form extensive communities, as do the 

 salt marsh fucoids in the northern hemisphere, but it is the only 

 known representative of the limicolous fucaceae in the south. 

 As a group the marsh fucoids are characterized by : 

 (i) Vegetative reproduction as the common means of perpetua- 

 tion. 



(2) Absence of any definite attachment disc. 



(3) Dwarf habit. 



(4) Curling or spirality of the thallus. 



(5) In the species derived from Pehetia, Fucus vesicolosus and 

 F. spiralis that have been investigated it has been found that 

 the three-sided juvenile condition of the apical cell is re- 

 tained throughout life. The cryptostomata are marginal and 

 division in the megasporangia is only partial or else does not 

 occur. It is suggested that these features are due to : 



(a) exposure, which results in a dwarfing of the thallus ; 

 {h) lack of nutrient salts which induces a narrow thallus ; 

 (J) the procumbent habit and consequent contact with soil 

 causes spirality because growth takes place more rapidly 

 on the side touching the soil. 

 The cause of steriUty may either be a result of the high humidity 

 (according to Baker, 1912, 1915) or, more probably, because of the 

 persistence of the juvenile condition as represented by the apical 

 cell and cryptostomata. The marsh fucoids occur most frequendy 



