the Marine Algce of the Firth of Forth. 463 



(6) As m my Bhodophycece are found growing upon the 

 carapaces of living Crustacea, it follows that a more 

 extended range than might otherwise occur may thus be 

 acquired by a given species. It is noteworthy, however, 

 that in such cases the sizes are invariably small. 



(7) Although more difficult to determine, it cannot be 

 doubted that the density and pressure of the water exercise 

 an important influence. The effect of these factors is 

 perhaps more readily seen by observing the ciianges in 

 general habit assumed by species as they acquire lower 

 levels, or by comparing certain species exposed to different 

 salinities at corresponding levels. 



In this connection the following statement by Meneghini* 

 may be quoted : — " The very striking difference between the 

 marine vegetation of the coast of Norway and that of the 

 Baltic is due, according to J. G. Agardh, to the different 

 degree of salinity of these two seas." The author adds 

 in a footnote : — " It has been universally recognised by 

 chemists that on this account the algae of the Baltic 

 contain a less proportion of iodine than those from seas of 

 which the salinity is greater." 



(8) Temperature has a direct influence on the time of 

 emission of swarmspores, and generally on the rapidity of 

 maturation of the fruit. In mild seasons the emission of 

 such spores continues longer than usual (e.g., in Ecto- 

 carpus siliculosus, &c.). In the Florideae the maturation 

 of the antherozoids is hastened, and the formation of the 

 cystocarp takes place earlier, and may continue later than 

 usual. If specimens of the same species from different 

 levels are compared, the influence of longer exposure to 

 strong sunshine {e.g., in shallow pools near the level of 

 high tide), is manifested by a somewhat earlier discharge 

 of spores (see p. 425), Specimens of Ectocarjnis {E. 

 siliculosus and E. littoralis) from such pools have been 

 compared in this respect with others from deep dark pools 

 at the level of low tide, and in all cases the spores were 

 found to be emitted from the former somewhat earlier 

 than from the latter ; Monostroma latissimum, Ulva linza, 

 Enteromorpha intestinalis, E. compressa have been observed 

 to illustrate the same rule. 



* Meneghini, op. cit., pp. 50, 51. 



