464 Mr Rattray on the DistrihUion of 



(9) Kapid and irregular currents are unfavourable for 

 extending distribution. This is well seen in the case of 

 the comparatively unproductive almost perpendicular sides 

 of the Bass Eock and the western side of the May Island, 

 as well as in many other parts of the coast of the main- 

 land, which are at all times exposed to the full force of the 

 waves from deep water. The result is the removal of 

 algse from their substratum by the destruction of their 

 rhizoids, or the destruction of the thalli, and the preven- 

 tion of the maturation of fruit. Stunted growth is almost 

 invariably found in such places. Specimens of Povpliyra 

 vulgaris, growing in an exposed situation on the Bass 

 Rock, were examined with respect to the maturation and 

 emission of spores at a time when other species on sheltered 

 spots on the island of Fidra were found to be ripe. No 

 signs of maturity were found, however, although the cells 

 of the stunted thallus were intact, and had the normal 

 appearance of those in a healthy plant. Even in rocky 

 areas, the bare exposed places carry fewer plants be- 

 longing to fewer genera than do the more sheltered 

 crevices or crannies. 



(10) The bright colour of some sea- weeds seems to 

 attract a number of animals, which aid in bringing about 

 cross fertilisation, e.g., marine Infusoria. Moreover, the 

 movements of minute Crustacea and other small animals 

 tend in the same direction. 



(11) The effects of light are twofold — (a) it influences 

 the swarmspores immediately subsequent to their emis- 

 sion ; and (6) it affects the physiological activities of the 

 mature plants. No observations have as yet been made on 

 the penetrability of luminous rays into the extensive 

 waters of the Forth, but from the large amount of sus- 

 pended matter in the water, which, moreover, varies very 

 greatly in amount at different times, it cannot be doubted 

 that the rays that reach those algae growing in the deeper 

 parts also vary correspondingly in intensity, while all the 

 dredgings that have been made go to show that it is those 

 algge whose colour is of the brightest red that occur at the 

 greatest depths. These are succeeded by sherry-coloured 

 species and by Phaeophycese, in shallower, and therefore, on 

 the whole, more luminous parts ; while they, in turn, give 



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