15 78 Proceedings of the Royal Irish Academy. 



III. — The Salt-Marsh Formation. 



The conditions obtaining on the salt-marsh resemble those of the sand-, 

 rather than the rock-formation ; but they differ in several important 

 particulars. In the first place, the salt-marsh formation is situated above 

 the level of high-water at ordinary neap-tides ; and in the second, the 

 substratum contains more or less humus consisting of mud or alluvial 

 deposits, and in the Clare Island area peat is frequent. By reason of its 

 bathymetric position, the marsh is only flooded at spring-tides, and hence the 

 algal vegetation instead of being moistened daily by the tide is liable to 

 desiccation on the one hand, and to prolonged soakings of fresh-water in the 

 form of rain on the other. Further, there is continual competition with 

 flowering-plants. As a result of the edaphic conditions, we find that the 

 algae are not attached by a basal disk as in saxicolous plants, nor are they 

 completely buried as is the case with many psammophilous species ; but they 

 either lie loosely on the substratum or are apparently rooted in the ground, 

 after the manner of flowering-plants. The lack of fully saline conditions 

 shows itself in the predominance of brackish species, green and blue-green 

 algae being abundant. The salt-marsh often passes by easy transitions to 

 sandy shores, mud-flats, or to the banks of rivers. 



From the floristic standpoint, the algae of the salt-marsh are generally 

 uninteresting; but among the Fucaceae remarkable forms occur, several of 

 which have long taxed the energies of systematists ; but with increased 

 attention to ecological considerations their elucidation appears more hopeful. 

 The Florideae are represented (amongst macroscopic forms at all events) by 

 two species only, viz., Catenella Opuntia and Bostrychia scorpioides. 

 Cyanophyceae are abundant ; and as far as filamentous genera are concerned, 

 they fall into fairly well-marked species ; the chroococcaceous series have not 

 been specially examined. Phoeophyceae are often conspicuous, and figure 

 largely as regards bulk, being represented almost entirely by members of the 

 Fucaceae. The latter vary widely in different localities, and are often of 

 considerable interest. The Chlorophyceae are well represented ; and, as is usual 

 under brackish conditions, they are often difficult to determine, lihizoclonium, 

 Chaetomorpha, and the smaller species of Enteromorpha are abundant, and 

 show much variation in form. These green algae are doubtless largely 

 modified by the peculiar conditions of the salt-marsh — a result which is not 

 surprising, when one considers the profound modifications amongst the less 

 plastic group of the Fucaceae. The variation displayed by Enteromorpha 

 intestinalis on flat shores when fresh-water is present is most extraordinary. 

 With regard to edaphic conditions, a certain amount of variety will be found 



