Clare Island Survey — Marine A Ig ae. 15 6i 



where there is a strong current, and is found typically in the channels of 

 3 to 5 fathoms between the outer islands. It consists entirely of L. digitata. 

 The bottom is scoured by the tide ; but the larger stones and blocks of rock 

 support a vigorous growth. The plants are remarkably strong, and in the 

 deeper parts the fronds often attain a great length. Epiphytic species are 

 few ; but in such localities the peculiar plant known as Rhodymcnia palmata 

 var. samiensis is occasionally met with. The third type of Laminaria 

 vegetation, characterized by the presence of L. Cloustoni in addition to 

 L. digitata, is found only outside the islands. It extends over large areas 

 in about 7 fathoms, and passes gradually into the exposed vegetation that 

 occurs further out. 



Representatives of these same sub-associations are found elsewhere. 

 L. digitata is abundant near the south entrance of Achill Sound ; and in the 

 quiet waters of Bellacragher Bay a distinct L. saccharina vegetation exists, 

 which in several places extends to the shore. In other countries, the sheltered 

 type of Laminaria vegetation has not received much attention. In the 

 Faeroes it is well developed, and shows similar variations to those in Clew 

 Bay, though with floristic differences. L. facroensis takes the place of 

 L. saccharina in quiet bays, and L. Cloustoni forms the vegetation of channels. 

 The Laminaria zone described by Joubin ('09) includes patches of L. saccharina 

 attached to stones on a soft bottom, which obviously correspond to the 

 sub-association of that species dealt with above. 



Encrusting Alga Vegetation. 

 Occasionally found, but more often on exposed coasts (see p. 50). 



II. — Sand and Sandy-mud Formation. 



The present formation is characterized by a large quantity of movable 

 sand or sandy-mud, in which the vegetation is liable to be partially or 

 completely embedded. In its extreme form, the shore consists entirely of 

 this matrix, the algae being immersed in sand, forming, in fact, a sand-binding 

 community. But the sand formation passes by transitions into the 

 rock-formation on the one side, and to mud-flats on the other. 



As an example of a sand-binder we may take Microcoleus, whilst 

 Vaucheria Thuretii supplies an instance of a plant that fixes sandy-mud. 

 Both form extensive associations. Rhizoclonium riparium also may under 

 certain conditions form a surface-covering on a shore of pure sand. In the 

 majority of sand-beaches, however, all vegetation is absent and only begins to 

 show when solid ground is reached. Where low half -buried rocks occur a 



