mmumtff^m ■ 



108 



H. JONSSON 



appears to have extended too high upwards, and where, when the 

 weather is calm, it is not wetted daily by the sea at and about 

 neap-tide. On a warm summer's day Pelvetia can become so dry 

 in such places that, when gathered, it needs no further drying — 

 the same may also be the case with Fucus spiralis. The individuals 

 of Pelvetia which grow at that height, i. e. sometimes right up in 

 the Verrucaria maura-belt, are usually very small (about 2 cm. in 

 height) and occur closely pressed to the rock; then they are often 



Fig. 3. Pelvetia canaliculata above, Fucus spiralis below. Illustration of a typical Pelvetia- 

 Fucus-spiralis-commumiy. Reykjavik, Aug. 13, 1909. (From phot, by Hesselbo.) 



found especially in crevices, and the new fronds may bear a sur- 

 prisingly close resemblance to a rosette. Lower down, where the 

 vegetation is luxuriant, the plants are about 8 cm. in height. Pelvetia 

 is the smallest of the Fucacea? on these coasts; it differs from the 

 others not only by its small size, but also by its lighter, yellowish- 

 brown colour, and its channelled frond, etc. The channelled frond 

 must be useful to a plant which is so exposed to the desiccating 

 action of the air as is the case with Pelvetia, because, by reason of 

 their being rolled, the under-side of the fronds is less exposed to 

 wind and weather. 



It is characteristic of the zonal division of the Fucacea: on the 



