326 ECOLOGY OF SALT MARSHES 



wetter habitat at levels where normally conditions may be somewhat 

 dry. Some authors are not prepared to acknowledge the existence 

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

 sistent. 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. 



There are several interesting features concerning the pan flora'of 

 the Norfolk salt marshes which may conveniently be mentioned 

 here. There are two different types of salt pan, those with soft 

 floors and those with firm, the algal flora usually being confined to 

 the latter, although so far there is no explanation of this feature. On 

 the lower marshes the pan flora is commonly composed of Chloro- 

 phyceae, whilst with increasing marsh height the Chlorophycean 

 element decreases and the Cyanophycean element increases. A few 

 of the constituent members, e.g. MonostromUy are seasonal in 

 appearance, whilst on some marshes there are pans which contain 

 algae that are normally associated with a rocky shore, e.g. Col- 

 pomenia, 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. Com- 

 paring the Norfolk marsh flora with that of a rocky coast the 

 following two generalizations can be made : 



{a) Species that are littoral on a rocky coast are to be found 

 growing at lower levels, usually sublittoral, on the marsh coast. This 

 must be ascribed to the lack of a solid substrate at the higher levels 

 where they would normally grow. 



{b) Littoral species of the rocky coast are found growing at 

 higher levels on the marsh coast. This can be understood in the 

 case of those species living in pans or in the streams where they are 

 continually covered by water, but at present it is diflicult to provide 

 an explanation for the few species which actually grow on the 

 marshes. 



Turning now to the algal vegetation of the marshes proper. 

 Carter (1932, 1933) has suggested that on the Canvey and Dovey 



