1915.1 



SETCHELL DISTRIBUTION OF MARINE ALGAE 



293 



Australia the marine flora of the southeastern region is defi- 



es 



nitely set off from that of the southwestern region. 



These various points and regions will doubtless become 

 more definite and more of them will become established as 

 careful investigations of the floras are made. They un- 

 doubtedly indicate that thereabouts are changes in the con- 

 ditions regulating the separation of the general flora into its 

 larger divisions and are of great importance in any inquiry 

 as to the general factors affecting the distribution of marine 

 algae. 



Along with the mapping out of floras into regions, provinces, 

 etc., it seems best to consider, next, the factors which seem 

 to regulate the distribution. These have been considered by 

 Kjellman ('83) and by others, and are summed up by 

 Oltmanns ( '05). Particularly is it desirable to consider which 

 may be chiefly responsible for the limiting of the species 

 within the regions or provinces. 



The substratum exercises an important influence on the 

 attached flora or benthos and that is particularly the part of 

 the marine flora I intend to limit this paper to, since the 

 plankton brings in certain particular factors having to do 



with its floating habits. Of course, benthos can only exist 



on its proper firmer substratum and different species differ 

 in the nature of this. However, it is sufficiently evident that 

 the character of the substratum limits species only locally 

 and can by no means be considered as a factor in controlling 

 floral regions or even floral provinces. 



The motion of the water is a limiting factor in distribu- 

 tion, some algae preferring quiet water, some flowing, some 

 surge, etc., but this factor, too, is clearly a local and not a 

 general one in the distribution of the marine algal benthos. 



The specific gravity of sea-water varies and with it, of 

 course, its salt content. This variation, so far as marine 

 algae are concerned, varies from water only slightly brackish 

 to that (in case of exposed and shallow tide pools) of an 

 almost concentrated solution. There is a latitudinal zonal 

 difference here also, but it is not so great as may be found 

 in localities at no considerable distance from one another. It 



