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LAMINARIACEiE OF OKKNEY : 



Their Ecology and Economics. 



Br Magnus Spence 

 (Deerness, Orkney). 



Our Northern Seas round Orcades have long been noted for the 

 large amount of seaweed cast upon our shores. Two reasons may be 

 given for this : (1) the water is comparatively shallow, with rocky 

 ridges and sunken skerries here and there, on which Laminarias find a 

 congenial habitat ; (2) no part of the British area has so high a 

 record for gales as Orkney and Shetland, and there is little doubt that 

 the rough turmoil of the sea produces more vigoi'ous plants than the 

 quieter waters of the English Channel. The fact remains that for 

 beauty and luxuriance the larger Lauiinarians of Orkney are not sur- 

 passed by tliose of any other part of the British Isles, 



I. L,\MiNARiA Cloustoni Le Jobs. Two tangles have been con- 

 fused under the older name of L. dicjitaia L., as by Linnteus himself 

 and still older writers. These are conveniently known respectively as 

 L. Cloustoni and L.flexicaulis of Le Jolis. The old name L. digi- 

 tata might have been retained for the larger form, and was definitely 

 isolated for this type by Harvey (Phyc. Brit. pi. 228), beyond any 

 jiossible doubt; the other plant being isolated as var. stenopliylla 

 {[A. 888). But a more usual custom, based on herbarium specimens, 

 lias carried on the L. digitata to the ^m^Wev L. Jlexicaulis, since only 

 of this plant were specimens ever obtained small enough to go on the 

 herbarium sheets. To avoid confusion L. JiexicanUs admirably 

 expresses the distinctive feature of one form, while L. Oloustoni 

 {=L. hi/perborea oi Norwegian writers) is less fantastic, and com- 

 memorates Charles Clouston (1800-84), an Orkney algoh)gist. 



L. ffwicaulis is a tangle seen much less on northern shores than 

 L. Cloiiaioni : the latter is the common tangle in Orcadian waters. 

 It is known as the "Red Tangle," while the former is the "Black 

 Tangle." During last winter not more than five per cent, of the 

 tangles on the beach were L.flexicaulis^ but in May the propoi'tion 

 had risen to 15 per cent. By May the " Cuvy," as L. Cloustoni is 

 generally termed, had shed its frond, and the rough sea had less 

 ])ower to tear it from its hold-fast, which may easily account for the 

 difference per cent. The Red Tangle is really brown when fresh, but 

 when carted on the land as manure, and exposed to the rain and sun, 

 the fronds become red, and remain so after three months' exposure ; 

 hence the name. These two tangles occupy different zones of tidal 

 waters ; during spring tides L.flexicaulis is readily found growing 

 in ))ools and on the sea-bottom, before reaching the level of 

 L. Cloustoni ; the latter is never fully ex])osed, oidy the most stunted 

 steins at the higher level being found out of the water, and the tops 

 of the next lower down. At extreme low-tides they can be seen 

 ci'owded together in miniature forests ; growing in deeper water in 

 " close canopy," and bending in the break of heavy swell, in the 

 manner of a gust of wind passing over a field of corn. 



Journal of Botany. — Vol. 56. [Octorer, 1918.] u 



