Clare Island Survey— Marine Algae. 15 165 



in the North Atlantic. It is almost impossible to believe that 0. mucronulum 

 can have been introduced, as at least one herbarium specimen shows that it 

 has existed in S.W. Ireland for 100 years. At the same time, the pre- 

 ference of the plant for well-lighted pools, and the fact that it apparently 

 disappears in autumn, might be taken as an indication that it is a native of 

 a warmer region. That it was introduced from the British Isles to Australia 

 and New Zealand is out of the epiestion. For the present the plant must 

 remain a l'emarkable case amongst algae of discontinuous distribution. Its 

 precise range in the British Isles should be ascertained. When this is known 

 we will be in a better position to pronounce as to the status of the plant, and 

 to discover if it is spreading on our shores. From S. Devon and 8. Cornwall 

 it is (or was, a few years since) certainly absent, but the same cannot 

 be said of Wales, as that coast has not been carefully worked. It is abundant 

 in the Isle of Man ; but no records are known from the east and south of 

 Ireland. 



The best-known case of an alien alga in the British Isles is that of 

 Colpomcnia sinuosrt, which has been kept under observation in France and 

 England (Sauvageau, '07, Cotton, '08, '11). It is a conspicuous plant, and was 

 first observed both in France and England (Scilly Isles) in 1905. By 1909 it 

 had spread as far as Hampshire, and it occurs now in great profusion in 

 many parts of Cornwall, Devon, and Dorset. Colpomenia is specially adapted 

 for floating ; hence rapid colonization is comparatively easy. It affords an 

 example of a Mediterranean species adapting itself to the conditions of a colder 

 sea, and becoming naturalized at once. Codium mucronatum, on the other 

 hand, does not readily float, and is probably much less hardy. 



Bonnemaisonia hamifera provides another problem. It is known in Europe 

 from several places in the English Channel, and has always been regarded as 

 of Japanese origin. By means of its hooked branches it clings tenaciously to 

 floating weed, and is thus no doubt capable of being transported for a 

 considerable distance. Its occurrence on Clare Island was most unexpected, 

 and raises a doubt as to whether the plant after all is not indigenous to our 

 islands (see p. 136). On the other hand, there is the noteworthy fact that 

 it was not noted by McCalla nor by any other west-coast collector, and that 

 until 1895 it was unknown in Europe. If an introduction, it can hardly 

 have come direct to the west of Ireland; but as nothing is known as to its 

 presence or absence in the southern provinces, it is useless speculating as to 

 the method of transport or port of entry. 



Questions such as those raised above make us feel our lack of knowledge, 

 and emphasize the need of further study of our own flora. The vitality and 

 floating power of detached seaweed are likewise in need of investigation. A 



