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Clare Island Survey — Marine Algae. 15 83 



Vaucheria and Calothrix, which form a velvet-like growth of light and 

 dark green respectively, occur often in equal proportions ; but at times 

 Vaucheria is dominant. Ehizoclonium forms a dense felt, through which 

 emerge numerous plants of F. spiralis var. nana. At Achill Sound (as on 

 the banks of the Bunowen) a band of Rivularia Biasolettiana sometimes occurs 

 above Phoeococcus. An average reading would be as follows : — 



Feet. Inches. 



Rivularia Biasolettiana, .... 



Phoeococcus adnatus, .... 



Rivularia nitida, ..... 



Vaucheria and Calothrix, .... 



Ehizoclonium and F. spiralis var. nana, . 



When a vegetation-zone exists below the Rhizoclonium band, it consists of 

 Fnteromorpha intestinalis and F. spiralis, the latter being larger and stronger 

 than when it occurs at a higher level. 



A large number of readings were taken at Mulranny, Annagh Island, and 

 Achill, and, though the amount and luxuriance of the different species differed • 

 considerably, the general zonation was invariably the same. Neither was 

 any difference noticeable on the banks composed of loam, except for the fact 

 that F. spiralis was practically absent, the soil being apparently too soft for it 

 to obtain a foot-hold. 



The period of submersion can only be ascertained by observations on the 

 spot. At Achill Sound, the neap-tides reach the level of F. spiralis, though 

 the salt water soaks up through the peat to Vaucheria and Rivularia. With 

 spring-tides the whole vegetation is flooded, and one may see the top zone of 

 Phoeococcus covered with two feet of water. Slight variations due to local 

 topography are of course frequent. 



Comparing the above vegetation with that found on the banks of the 

 Bunowen, one notes that F. spiralis replaces F. ceranoides, and that Fntero- 

 morpha minima is absent. The upper zones are the same in both — a fact whicli 

 is easily understood when the source of moisture is considered. A similar 

 series of plant associations doubtless occurs in other districts where sheltered 

 banks exist. At Mersea Island (Essex) bands of Cyanophyceae in regular 

 sequence have been noted, but on a much smaller scale than at Achill. 

 The firm peat of the west of Ireland is doubtless more suitable for permanent 

 growth than the soft banks of the Essex coast. 



iv. River-Mouths and Fresh-water Streams. 



The method which has been adopted for describing the flora of previous 

 sections cannot easily be followed in dealing with the vegetation occurring at 



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