Tlie Distribution of Marine Algce. 421 



Apart from the large and important family of the 

 Diatomacese — some of the most curious and interesting of 

 which are not uncommon in the Firth of Forth — upwards 

 of three hundred species of marine or brackish water 

 Algse have till now been recorded in this locality, the 

 Chhrophi/cece, Phceo])hjcece, and Rhodophyccoe being all 

 well represented both in superficial and in bathymetrical 

 range. The widest superficial range must, however, be 

 assigned to the Chloroj^hycece^ of which representatives 

 occur as far up the Firth as the tidal influence is felt, 

 where they gradually merge into the typical green Algae of 

 fresh water, while not a few of the same species occur at 

 or a little above the tidal limits on the shores and beaches 

 waslied by the spray of the open ocean. The Fhceo- 

 phycece, though penetrating well up the estuary, mani- 

 festly improve both in luxuriance of growth and in fruit- 

 bearing capacity as the purer waters of the ocean are 

 approached, while the Floridem are pre-eminently the types 

 of truly oceanic plant vegetation. 



The haunts of estuarine sea-weeds are abundant and 

 various. For the most part they adhere to rocks or boulders 

 of very diverse characters — volcanic and sedimentary alike. 

 It may, however, be observed generally that rugged, rough, 

 creek-forming, or readily decomposable rocks, carry better 

 crops than perpendicular, smooth, or regularly outlined and 

 more resisting cliffs or boulders. The difiiculty which is 

 experienced by the motile spores in procuring a satisfac- 

 tory nidus on which they may become fully evolved is one 

 of the chief obstacles to be overcome in the latter case, 

 whether the smooth surface be the result of direct wave 

 impact against a stable cliff, or of the trituration of this by 

 shingle impelled against it by the force of the waves or 

 tidal currents, which often so disturb the smaller boulders, 

 that any vegetation likely to appear upon them is speedily 

 checked and ultimately destroyed. The occurrence, how- 

 ever, of several species belonging to different genera on 

 smooth boulders is often striking enough, e.^., in the case 

 of Hildcnhrandtia rubra, Balfsia verrucosa, various Mdo- 

 besice, Litlwthamnia, Prasiola marina, &c., and such in- 

 stances point to a period of quiescence, during which the 

 rocks or stones have not been exposed to violent wave or 



