100 H. JONSSON 



brown algae are found most abundantly, the green algae come next, 

 red algae occur less frequently, and blue-green algae are found in 

 the smallest quantity. The substratum is either rock — solid rock 

 or else talus of debris — or pebbles, or in many places consists 

 of gravel, clay or mud. The perennial species prefer almost 

 exclusively the rock-substratum; but they occur, though 

 very seldom, on other substrata, and are then, as a rule, dispersed 

 here and there on small stones, viz. on a gravel-clay soil at the 

 head of the fjords. The annual, short-lived species also occur most 

 frequently on a rock-substratum, but they also occur fairly frequently 

 on the pebbles of the littoral zone. 



1. The Prasiola stipitata-association. 



This association extends furthest upwards and is found well 

 developed on the rocks in several places round the coasts. It is 

 usually almost on a level with the Verrucaria-maura belt and, up- 

 wards, sometimes approaches the outposts of the land-vegetation. 

 At the highest water-level it is covered by the sea for a short period, 

 or is, at least, washed by the breaking waves; but such high water 

 occurs only rarely, and in normal conditions this association must, 

 without doubt, be content with the spray from the waves during 

 spring and summer. On less exposed coasts this association is, as 

 a rule, sharply defined from the community of filiform algae which 

 exists below, but on a very exposed coast the boundary is more 

 variable. 



The dominant species in this association is the small, leaf-like 

 Prasiola stipitata, which grows very socially upon the tops of flat 

 rocks. As it has its distribution almost exclusively in this belt it 

 seems natural to designate the association by its name. It is essen- 

 tially adapted to live in the air, and is capable of withstanding 

 desiccation well, which may be perceived, inter alia, by the fact 

 that it does not seek clefts and crevices but grows on surfaces 

 which are exposed to light, wind and weather. The density of the 

 vegetation must also afford each individual some protection against 

 desiccation. In spring and summer long periods must occur during 

 which this association is not wetted by the sea, and, during summer 

 drought, I have often seen Prasiola stipitata as dry as a bone upon 

 the rocks. Prasiola furfuracea also occurs side by side with this 

 species, but is rarer. 



Species and varieties of species, such as Enteromorpha intesti- 



