374 W. A. Setchell — Classification and Geographical 



the European shores during the forced southward migration at the 

 time of the Glacial Epoch. 



The southern polar waters are entirely open and the temperature 

 limits the species almost entirely as shown above. 



The Macrocystis being unusually well adapted to a floating exist- 

 ence has traveled up the western coasts of the Americas. Why it 

 is not reported from Japan seems a mystery. It extends down 

 along the shores of Kamts3hatka and it does not seem as if it could 

 be the temperature alone that keeps it from inhabiting the Japanese 

 coasts. 



There remains for discussion the existence of peculiar groups of 

 genera at different places in the North Pacific, concerning whose 

 origin, little that is at all satisfactory, can be said at present. 



In Behring Sea we have the group of the Agareae well developed 

 and represented not only b}^ Agarurn and Costaria^ but also by the 

 endemic genera, TIiaJassiophyllinn^CymatlicBre^ and Arthrothamnus. 



On the Californian coast we have the three genera Postelsia, 

 Nereocystis, and Dictyoneiiron of the Lessonese, Eisenia of the 

 Ecklonese, Egregia sole representative of the Egregieae, and Ptery- 

 gophora of the Alarieae, all of which are nearly if not quite confined 

 to California. 



In Japan the Eckione?e are represented by the peculiar genus 

 Ulopteryx and three endemic species of Ecldonia itself. 



In connection with the study of the classification and the distribu- 

 tion of the various subtribes, there arises curiosity regarding the 

 origin of the various forms and their relationships to one another. 



If we believe that the various species of the Laminariaceae form a 

 natural group and are phylogenetically connected, then it becomes a 

 matter of interest as to which form is least differentiated from the 

 archetype or ancestral form of the whole group. Very naturally 

 we might look among the Laminarieae for such a form. Chorda is, 

 perhapj", the simplest form, but it differs so decidedlyin form and 

 structure from the ordinary species that it may be questioned 

 whether w^e should include it in the Larainariaceas at all. Sacco- 

 rhiza dermatodea (DelaPyl), J, Ag. is of very simple form and 

 structure and much more nearly related to the rest of the kelps. 

 Yet in structure it presents so many peculiarities that we may be 

 compelled perhaps to look upon it as considerably differentiated 

 from the primitive type of the group. 



