the Marine Algco of the Firth of Forth. 425 



well as many other forms, illustrate the same law. The 

 large growths of Leathesicc (e.g., L. tuheriformis) , found on 

 patches of CoraUina officinalis, as well as of Folysiphonio) 

 (e.g., P. fastigiatd) on Fucus nodosus, and other cases of 

 Epiphytism, likewise go to show that in such instances this 

 peculiar association is not prevented hut aided by such 

 conditions. These phenomena are most easily studied in 

 undisturbed parts of the shore and on the islands, being 

 well illustrated on may parts of the May Island, Inchkeith, 

 and Fidra, and in many unfrequented shore pools on the 

 mainland. 



While some Algse grow to great advantage on rocks in 

 deep pools of clear water, many others are especially com- 

 mon in shallow and exposed pools. Various Ceramia, 

 Ftilotas, Folysiphonice, Gallithamnion ])lumula, and G. gra- 

 cillimum, may be chosen as examples of the former group, 

 and among others Halidrys siliquosa, Rivularia atra^ 

 Ulva linza, Monostroma latissima, Sphacelaria cirrhosa, 

 Symploca harveyi, Asperococcus echinatus, Ectocarpus 

 silicidosus, F. littoralis, CoraUina officinalis^ Myriotrichia 

 clavceformis, Conferva tortuosa, &c., of the latter. The 

 somewhat rapid changes at once of exposure to light 

 and of temperature, do not in either case act in a detri- 

 mental manner to growth ; on the contrary, although in 

 brilliant summer sunshine the temperature of such shallow 

 pools may become relatively very high,* the formation 

 and maturation of fruit occurs quite freely, and in still 

 conditions a very copious evolution of gases takes place. 

 In many cases, e.g., Ectocarpi, Enter omorphce, 3Io7iostromai, 

 Sphacela^noe, &c., an elevation of temperature continued 

 for even a short period accelerates the escape of swarm- 

 spores, it may be even by some days. Thus specimens of 

 Enteromorpha compressa, gathered in the beginning of Sep- 

 tember in a fertile condition, have been experimented with 

 in different thermal conditions. Some specimens, exposed 

 to the ordinary external conditions in glass vessels unpro- 

 tected in any manner, were found to give out swarmspores 

 on the sixth day after collection, the average temperature 

 during the day being 64° F., and during the night 51° F. ; 



* During very warm summer days the temperature of shallow high water 

 pools have been found at low tide to be 15° F. above that of the tidal ocean water. 



