4 



Göte Turesson 



will be shown that the prostrate habit of shore plants may be in some plants a 

 reaction form called forth by a definite habitat factor while in others this morpho- 

 logical peculiarity is a fixed congenital feature. The plagiotropic growthform on 

 exposed sea shores is thus made up of both modificatory and hereditary characters, 

 as will be further demonstrated later. As the physiognomy of the shore vege- 

 tation may be iutiuenced to a large extent by the plagiotropic growth- form, the 

 knowledge of the actual composition of the shore vegetation and of the different 

 degree of plagiotropy in the different zones of the beach in the region studied 

 becomes of interest, and will receive some attention. 



1. Physiognomy of the shore vegetation. 



Although plagiotropic shore plants may be found almost anywhere along 

 our coasts, exposed sandy shores are richer in such forms than protected ones, for 

 reasons to be mentioned later. Consequently, the best examples of this type in 

 our country are to be found on the west coast. The shore line at and north of 

 Kullen as well as the much exposed Hallands Väderö, a small island lying off the 

 coast of Skåne, are excellent localities for this growth-form. The following data on 

 the shore vegetation have been collected in that region, but the plants listed are 

 typical of almost the entire west coast of Sweden. As to the terminology followed 

 in dividing up the plant-covering into vegetational groups the classification of Ser- 

 NANDER (23) has been used. This writer distinguishes between the littoral belt lying 

 below the normal high-tide line, and the supralittoral belt lying above this line. 

 A third belt, the epilittoral, is superimposed on the supralittoral. The vegetation 

 of this belt shows only indirect signs of the vicinity of the sea (influence of strong 

 winds, impregnation by atmospheric sodium chloride etc.). The gnarled wind- 

 broken woods along exposed shores belong to this belt. The supralittoral belt is 

 divided into a lower supralittoral zone and an upper siipralittoral zone. The former 

 zone corresponds with the Maura-hoii of Warming (30) and with »die Wellengürtel» 

 of Häyrén (7). The latter zone has been called the Placodium-h%\i by Warming 

 and »die Spritzgürtel» by Häyrén. Corresponding belts or zones have also been 

 distinguished by some American writers, among which those given by Transeau (25) 

 for Cold Spring Harbor, Long Island, are well known to American and English 

 plant-geographers. As his classification is almost identical with that given by Sek- 

 NANDER and used in this paper it may be well to compare the two. The Lower 

 Beach of Transeau is the portion worked over by the summer waves and corresponds 

 closely with the area between the lowest and highest summer tide lines. This zone 

 corresponds with Sebnander's littoral belt. The Middle Beach, defined by the still 

 higher level attained by the waves during the storms of winter, is identical with 

 the supralittoral belt of Sernander, and the Upper Beach with his epilittoral. 



