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178 ERIK SKYEpredominating the field layer (cf. APPELROTH 1948).Here and there the coastal forests are broken bylarge or small boulder fields, whose vegetation ischaracterized by epilithic lichens and a verysparse tree layer, consisting chiefly of stunted pinesor in certain places multistemmed scrubby spruces.There is generally no continuous alder border onboulder-covered shores deficient in fine material.Here the alder bushes come singly and grow ratherslowly. Of all the woody species on boulder shoresthe rowan, Sorbus aucuparia, appears to be thehardiest. Pine and spruce commonly appear at thesame time. In the latter growth is often stunteddue to the fact that the leading shoots die off. Onsuch shores the spruce displays a remarkable capacityof "layering", i.e. developing adventitionsrooting from its soil-bound lowest branches. Whenthe original top-shoot has died one or several of thebranches turn to grow upwards and new stems areformed. When these have been killed new branchestake over, until a large clone is formed. Probablythe protruding shoots are killed by the salty sprayespecially during the winter half year, in combinationwith frost-drought. The spruce does betterthan the pine, which is heavily beaten by thewind and develops a one-sided crown. Where it istoo severely exposed the pine may form a latticeover the boulders and rocks (HXYREN 1900, 1940,BRENNER 1921, SKYE 1963).SANDY SHORES.-Where the shore consists ofsandy beaches the pine often forms the first generation.However, in the southern part of Gastrikland(and occasionally elsewhere) it is usually precededby H ippophae rhamnoides, which has a preferencefor newly formed mineral soil. The distributionof this species is very irregular but it occurs allalong the coast. In certain cases sandy beaches, too,have a border of alders mixed with such elementsas rowan, birch, Salix, spruce and pine. The undergrowththen often abounds in the following plants:Filipendula ulmariaRubus idaeusMyrica galeRumex acetosaP otentilla palustrisTrientalis europaeaGalium palustreEuphrasia frigidaViola rivinianaIn these sandy areas the pine often has a broadcrown and therefore shades its own · roots whichseems to be a useful adaptation. But it may as wellbe only an effect of the negative selection attributedto the activities of the 19th century sawmills, ormerely a modification induced by factors such asplenty of space, strong winds and meagre soil.As a rule the sandy beaches have a sparse vegetation.Common components areLathyrus maritimusElymus arenariusFestuca ovinaPuccinellia retroflexaTwo plants with peculiar disjunct ranges areLigusticum scoticum, encountered near Gavle andon the island of Storjungfrun but with its mainSwedish range on the West Coast, and Cardaminopsispetraea, found on the coast of Angermanlandbut also in the mountainous area of southernNorway and in eastern Karelia.MARSHES.-Where there are enough loose sedimentsthe alder border is often adjoined by moistbrackish marshes including, beside numerous seedlingsof alder, amongst othersOarex glareosaOarex M ackenzieiJ uncus GerardiEleocharis uniglumisGlaux maritimaOphioglossum vulgatumAster tripoliumSpergula salinaDeschampsia bottnicaTriglochin maritimumIn some sheltered bays there are fairly tall reedsof Phragmites communis and Scirpus Tabernaemontani.The shores of Vasterbotten and Norrbotten differbotanically in several respects. In particular, theyshow a larger proportion of the typical Bothnianelement: northern disjuncts, such as PotentillaEgedii and Primula sibirica v. finmarchica, andfreshwater species (see further JuLIN's paper).RocKY SHORES.-Another characteristic type ofcoastal forest is pine forest growing in fissureson bedrock. The tree layer mainly consists of pine,but spruce and birch may also occur. The treesare low and grow slowly, and especially the pinesare often grotesquely twisted. There is usually nofield layer and the bottom layer is often broken..Acta Phytogeogr. Suec. 50