126 H. JONSSON 



small pools, often forms a continuous fringe, the upper branches 

 either reaching to or lying on the surface of the water. In such 

 pools Chcetomorpha tortuosa sometimes occurs in fair abundance 

 loose upon the surface of the water; its filaments are usually densely 

 matted together. 



Fucus inflates f. linearis grows even more socially. At times it 

 is almost the dominant species in the smaller pools, although, rather 

 frequently, several other species are found intermingled with it. 

 This form is a biological variety of Fucus in flatus which, in the 

 pools, exists evidently under less favourable circumstances; this is 

 one cause of its small size and feeble structure, although another 

 is that it is not exposed, to any extent worthy of mention, to the 

 beat of the waves. Rosenvinge has especially shown this to be 

 the case as regards Greenland. Rosenvinge explains the frequent 

 occurrence of this form in the pools by the fact that the eggs of 

 F. inflatus are carried into the water-filled depressions by the move- 

 ment of the water and accumulate there. This explanation is un- 

 doubtedly correct, and, as Rosenvinge points out, all intermediate 

 stages between the feeble pool-form and the typical form can be 

 demonstrated. To any one who has seen this endless variation in 

 nature, it seems so certain that it is due to the influence of outside 

 factors, that experimental proof is almost superfluous. 



The uppermost pools are generally extremely poor in species ; 

 and, besides those already mentioned, only Enteromorpha inlestinalis 

 occurs in any great abundance. Where the coast is exposed, the 

 uppermost pools may, however, have a resemblance to the lower 

 ones of the upper littoral zone — a natural consequence of the 

 exposure. On more exposed parts of the coast a fringe of small 

 Monostroma Grevillei is often found, almost on the surface of the 

 water itself. At one place in E. Iceland I took the temperature of 

 such a submerged plant-covering, and the thermometer showed 

 20° C. (June 13). The vegetation was also somewhat injured, and 

 evidently did not prosper under these conditions. 



High up on a rocky coast to the south of Vattarnes in E. Ice- 

 land, I came across a pool-vegetation. I did not measure the alti- 

 tude of the spot, but I do not think that I was greatly mistaken 

 in estimating it at 70 — 100 feet above sea-level. As regards the place, 

 I noted in my dairy — "High rocky coast, land-plants grew round 

 the alga-pools. The water in the pools must be replenished with 

 rain and heavy surf, which sometimes fail for long periods during 



