272 TRANSACTIONS OF THE [Sess. lxxviii. 



between ebb and flow. Where, however, sandstone rocks 

 occur, they shelve more steeply, and it is noticeable that 

 on them the brown seaweeds are scantily represented, 

 large ledges of the rock remaining quite devoid of vegeta- 

 tion, while those portions which are covered are chiefly 

 occupied in the lower zones by Gigartina, and higher up 

 by Cladophora and Enter omorpha. 



One marked difference in the dominance of species 

 distinguishes the distribution of the algae at Toward Point 

 from that in Loch Striven. All round the Point at low 

 spring tides, occupying yards of ground both above and 

 below the water's edge, there becomes exposed what might 

 be taken as the very home of Laminaria digitata, Linn. 

 Quantities of its yellow-brown thallus protrude from the 

 shallow sea beyond low- water mark, while innumerable 

 holdfasts and thallus " stalks " are exposed on the damp 

 rocks, standing up like the stumps of some strange marine 

 forest, and suggesting, in the contrast of general habit with 

 that of the algae next above, the possibility of still further 

 variations in growth-form or dominance of species in that 

 unknown world below the waters which even the lowest 

 tides do not reveal. 



The three groups of Chlorophyceae, Phaeophyceae, and 

 Rhodophyceae are thus all well represented, the Greens 

 occupying the highest zone and the Reds the lowest, while 

 they overlap to a large extent between the two extremes 

 in the distribution of Cladopltora and Gigartina. The 

 Browns, on the other hand, extend in a series of species 

 across the whole region between the tide marks. 



Concluding Remarks. 



The account which has been given does not pretend to be 

 exhaustive. Mention of many less common species has 

 been purposely omitted in order to avoid undue extension 

 of mere lists of plants, and because it is felt that the 

 frequency of a species rather than its rarity is what gives 

 it a claim to the notice of the ecologist. The primary aim 

 has been to describe the grouping of the characteristic 

 plants and the situations which they occupy, while at the 

 same time keeping in view how these, taken as particular 



