THE LAW OF TEMPERATURE CONNECTED WITH 

 THE DISTRIBUTION OF THE MARINE ALGAE 



WILLIAM ALBERT SETCHELL 



University of California 



What I have to bring before you is simply a preliminary 

 consideration of the general subject of the geographical dis- 

 tribution of the marine algae together with some inquiry into 

 the conditions immediately affecting such distribution and as 

 possibly effecting a segregation into the larger units. In 

 accordance with such an intention, I have started a tabula- 

 tion of all the marine species and varieties, which is far from 

 being completed as yet, but which has, however, reached a 

 stage at which certain general statements may be made as to 

 probable results. 



The geographical distribution of the marine algae has been 

 treated of in various ways and in many papers. It is more 

 or less customary to make a comparison between a particular 

 flora and other more or less corresponding floras in com- 

 parative tables, percentages of common and endemic species, 

 etc. Certain speculations, based on such data, as to the 

 origin of certain algal floras have also been indulged in. The 

 result is that we have certain geographical areas fairly well 

 marked out and certain others more or less indistinctly out- 

 lined or surmised. Certain ecologic classifications have been 

 proposed, particularly as to zonal occurrence in varying depth, 

 influence of varying degrees of salinity, character of the sub- 

 stratum, influence of surge, quiet waters, etc. Very little 

 attention, however, has been paid to general factors control- 

 ling distribution over larger areas. We speak broadly of 

 tropica] species, or of arctic or antarctic species, of temperate 

 species, etc., but no attempt has been made to survey the 

 distribution of marine algae in general throughout the oceans 

 and seas of the world and to attempt to determine the limit- 

 ing factors segregating one large area from another. An 

 attempt to determine how far our present knowledge of 



Ann. Mo. Bot. Gard., Vol. 2, 1915 



(287) 



