Clare Island Survey — Marine Algae. 15 15 



which is regulated by the exposure and lie of' the rocks), but shade and 

 terrestrial moisture are also important. The associations, moreover, found 

 in this area are the same as those in the upper part of the littoral region, and 

 often merely extensions of them. I therefore agree with Borgesen in not 

 regarding it as a separate region. 



With regard to the lower limit of the littoral area, on exposed coasts the 

 low-water mark at neap-tide is certainly the natural line of demarkation. 

 At the same time, on a calm day during spring-tides, the Laminaria and 

 Alalia growth may be exposed, and become dry for a short time ; but this 

 is obviously exceptional. On sheltered shores the boundary-line is not 

 so clearly marked; and it is difficult to define the beginning of the sub- 

 littoral vegetation. In Clew Bay it is particularly perplexing ; and the 

 flatter the shore, the less marked is the boundary. As time did not allow 

 of special work on this point, the lower limit of the littoral region has 

 been made uniform with that on exposed coasts — namely, the ebb-mark at 

 neap-tide. 



B. — The Formations and Associations. 



A good deal of confusion exists with regard to the terms ' Formation ' 

 and ' Association.' Kjellman first introduced the word ' Formation ' into 

 algological literature in his paper on the algological communities of the 

 Skager Back ('78). He describes an algal formation as a small portion of 

 the whole algal vegetation which is distinguished by a characteristic 

 " Yegetations-Geprage," adding that in a general way these portions of the 

 vegetation obtain their characteristic stamp through one or more algae that 

 predominate. Most other writers have followed Kjellmann's nomenclature. 

 It is, however, more in accordance with the terminology now generally 

 employed to use the term ' association ' for these communities, and to 

 reserve the term ' formation ' for communities which occur together in a 

 definite type of habitat. The substitution of the former term for the latter 

 was first put forward by Borgesen ('05), and the name ' formation ' was 

 at the same time employed by him for " associations when united together 

 under the same or nearly the same ecological conditions." Examples 

 of Borgesen's formations are the Chlorophyceae, the Fucaceae, and the 

 Laminaria communities of exposed coasts. Kylin ('07) does not follow this 

 nomenclature, but adheres to the term ' formation ' with the meaning- 

 attached to it by Kjellmann. Jonsson ('10), on the other hand, follows 

 Borgesen. 



Borgesen's use of the term ' association ' is certainly more correct ; but the 



