Glare island Survey — Marine Algae. 15 169 



Ireland must be highly speculative, since our knowledge of the rapidity with 

 which algae extend their range is very meagre, and fossil evidence (with 

 regard to our area) is absolutely wanting. For this reason the most important 

 data are those furnished by the study of the general distribution of the species, 

 and by a recognition, if possible, of the presence of any definite phyto- 

 geographic groups. Borgesen ('05, p. 805) has summarized the views 

 propounded by Kjellmann and Reinke as to the origin of the North Atlantic 

 algal flora, which, in a word, is said to consist of a mixture of old atlantic and 

 arctic elements. The question of the survival of plant-life in Ireland during 

 the Ice Age, as to which there is so much difference of opinion, I leave to 

 others, and will confine my remarks to phytogeographic observations, and to 

 features in the Clare Island flora which appear to be of interest. Such may 

 be of service to those engaged in the study of the antecedents of the present 

 Irish fauna and flora. 



Although the flora contains a decidedly larger proportion of southern 

 forms than corresponding areas in England and Wales, there appears to be no 

 element, such as is found amongst Phanerogams, which is strikingly austral. 

 The southern species extend, probably without exception, along the south 

 Irish coast, and are found in Devon, Cornwall, and Brittany ; many also 

 occur in the Bay of Biscay and on the north coast of Spain. Their range 

 being continuous is, therefore, not remarkable. No notably Spanish or 

 Mediterranean species are found. A boreal element of a special character is, 

 on the other hand, recognizable, the abundance of Callithamnion arbuscula and 

 Ptilota plumosa being very striking in an area where the general facies is of 

 a much more southern type. Neither of these species occurs in the south of 

 England, nor have they been recorded south of Yorkshire and Anglesea. 

 Their position on the Irish west coast is, however, not isolated, but is merely 

 a continuous southern extension of their range. But, as a result, there is in 

 the marine flora, as in the terrestrial, a distinct mingling of north and south. 

 Other boreal algae might be mentioned ; but these are not so abundant, nor 

 has their distribution been so carefully ascertained. 



The presence on the west coast of Ireland of a boreal element which is 

 absent from the south of England, is a familiar problem to the Irish botanist. 

 In the case of the algae cited above, the question of a land-connexion between 

 England and Ireland need not be discussed, since the plants already occur in 

 the northern part of Great Britain. It would appear, therefore, that the 

 climatic or other conditions of the southern counties are unfavourable for the 

 growth of these species. With regard to climatic factors, it is well known 

 that extremes are more important than the mean ; and from this we might 

 conclude that, in the equable climate of Ireland, the maximum temperature 



B.I.A. PROC, VOL. XXXI. Y 15 



