236 PROCEEDINGS OF THE AMERICAN ACADEMY. 



in the Biscay region is noticeable, but not easy to account for. The 

 high percentage of brown algae in New England and Great Britain is 

 due to their northern latitude, these plants becoming increasingly preva- 

 lent as we go from the equator to the poles ; in actual arctic waters they 

 constitute the most conspicuous element of the flora. 



Table No. IV. shows the number of species common to the flora of 

 Jamaica and the other floras respectively ; No. V. shows the per cent of 

 each class of the Jamaica flora which is found in each of the other floras ; 

 No. VI. the per cent of each of the others found in Jamaica. A thor- 

 oughly explored country shows a larger per cent in No. V., a smaller per 

 cent in No. VI. than a region less known, but certain general deductions 

 can be made. The Puerto Rican flora is closely allied to the Jamaican, 

 69 percent being common to the latter; further exploration would proba- 

 bly increase rather than reduce this. The Canaries come next, and it is 

 noticeable that the percentage in Table No. V. is nearly the same in green, 

 brown, and red algae. In Table VI., which is perhaps the one best show- 

 ing the relationships, the common elements in the European floras grow 

 regularly less as the distance increases, only 8 per cent of the flora of 

 Great Britain being found in Jamaica. 



The Schizophyceae seem to vary least in different regions, the other 

 classes coming, Chlorophyceae, Rhodophyceae, Pliaeophyceae, the com- 

 mon per cent of the latter being surprisingly small outside of Puerto Rico 

 and the Canaries. 



It is worth noting that Jamaica and the Canaries have 66 species in 

 common, being 30 per cent of the former and 24 per cent of the latter ; 

 while New England and Great Britain, at about the same distance, have 

 258 in common, being 60 per cent for the former, 35 for the latter. 

 This merely illustrates the general rule that beginning almost identical, 

 in the Arctic Ocean, the floras of the two shores of the Atlantic diverge 

 increasingly as we go south. There are, however, a few species common 

 to Jamaica and the Canaries which have not apparently been found on 

 the mainland of either continent ; these probably represent an actual 

 communication between the two. 



Of the 34 fresh water algae, all but 2 are found in Europe, quite in 

 conformity with the rule that the fresh water algae of the two continents, 

 though separated by salt water, in which they cannot exist, are much 

 more alike than the marine algae, inhabiting the two shores of the 

 Atlantic. 



