352 THE ALGAE 



either as pioneers on the lowest marshes or else as an undergrowth 

 to the phanerogams. 



Outside the salt marshes of England, the salt marshes of New 

 England and New Zealand possess communities comparable to 

 those found in Great Britain. In Table lo the limicolous Fucaceae 

 community in New Zealand refers to the free-Hving Hormosira, 

 Attention may also be drawn to the Gracilaria flagelliformis com- 

 munity which is widely distributed over mud flats and in mangrove 

 swamps in New Zealand. It probably also occurs in Australia and 

 would seem to be the only endemic southern hemisphere com- 

 munity so far recorded. The plants of Gracilaria are not originally 

 free Uving but are attached to shells of molluscs buried in the 

 mud. 



One of the more striking physiographical features of salt marshes 

 is the salt pan. The number, shape and size of these on the different 

 salt marshes varies very considerably, but they generally contain a 

 certain number of algae, especially those pans which occur on the 

 lower marshes. They are important because they provide a much 

 wetter habitat at levels where normally conditions may be some- 

 what dry. Some authors are not prepared to acknowledge the exist- 

 ence of a pan flora because they maintain that the plants are not 

 persistent. A continual study of pans in one area over a considerable 

 period of time by the present author showed that a definite pan 

 flora did exist from year to year, and that many of the species com- 

 prising it reproduce during the course of their existence. The mere 

 fact that they can carry out normal reproduction would seem to 

 validate the recognition of such a flora. 



On the lower marshes the pan flora is commonly composed of 

 Chlorophyceae, whilst with increasing marsh height the Chloro- 

 phycean element decreases and the Myxophycean element in- 

 creases. A few of the constituent members, e.g. Monostroma, are 

 seasonal in appearance, whilst on some marshes there are pans 

 which contain algae that are normally associated with a rocky shore, 

 e.g. Colpomenia^ Polysiphonia, Striaria. These persist from year to 

 year in spite of the stagnant conditions, and when compared with 

 the habitats occupied by the same species on a rocky coast it is 

 found that they are probably growing at an unusually high level. 

 A comparison of the Norfolk marsh flora with that of a comparable 

 rocky coast leads to two generahzations which are probably vaUd 

 for other marsh areas elsewhere: 



