the, Marine Algce uf the Firth of Forth. 447 



is veiy striking. Species of Ectocarpiis {E. littoralis, E. 

 granulosus, E. fasiculatus, E. siliculosus, E. sphccro2}horus, 

 and E. tomentosus are now not iinfrequent, and speci- 

 mens of the somewhat similar Elachistea are common. 

 Lithothamnion polymorphum and Melohesia jnistulata are 

 common in many places on the rocks, whilst Mesogloia 

 vermicularis here reaches its uppermost limits. Many fine 

 Polysijjhonicv occur (notably P. urceolata, P. nigrescens, P. 

 atro-ruhescens, P. hrodicei, &c.), of these many elegant 

 forms are to be found in small but unexposed rivulets 

 of water between pools, as well as in pools themselves. 

 Porphyra amethystca, P. leucosticta, and P. vulgaris 

 are fairly common, and Pohjides rotimdus, as well as 

 Furcellaria fastigiata and Chondrus crispus, are very 

 abundant, Odonthcdia dentcda, though present, is of much 

 smaller size than in deeper water (e.g., off May Island, 

 Inchkeith, Fidra, <fec.). Schizymenia edtdis in the more 

 seaward parts is frequent, and often of large size. Rhodo- 

 mela suhfusca and R. Jycopodioides are also common in 

 many parts, even well up the estuary {e.g., at Inchmickery, 

 Inchcolm, &c.). Ptilota elegans is not uufrequent, though 

 of smaller size than in the previous zone or in still deeper 

 water. 



Here, moreover, a new feature is present in the occur- 

 rence of many forms of Chlorophycecv, among which are 

 Monostroma latissimurn, Porphyra ametliystea, and P. 

 leucosticta. The Enteromorpluc {E. compressa, E. intesti- 

 ncdis, E. erccta) here reach their lowest limits, and it is 

 noteworthy that the species diminish in size as they ap- 

 proach this limit. Two influences especially operate in 

 limiting the downward distribution of these forms, namely, 

 salinity and pressure. In specimens found at the lowest 

 limit swarmspores are produced somewhat later than in 

 others that occur at a high level, the plants are, moreover, 

 of a more stunted growth, and their texture is somewhat 

 more rigid. The influence of salinity is readily proved by 

 the circumstance that in no case do they extend to so 

 great depths, except along the course of streamlets of fresh 

 water as these enter the sea. By diversion of such stream- 

 lets for a considerable time the plants may be readily placed 

 in a condition of greater permanent salinity — their growth 



