EISENIA ARBOREA 161 



The second splitting, which must occur simultaneously 

 with, or very soon after the first, separates the meristera of 

 the blade longitudinally into two portions as has been shown 

 above. 



The peculiarities of the genus arise, then, from the sepa- 

 ration of the primary meristem into three parts one belong- 

 ing to the stipe and two belonging to the blade. Conse- 

 quently, the arms and ligules are blade rather than stipe 

 structures. 



That the blade raeristems may, under certain circum- 

 stances, divide again, is shown by the case of abnormal 

 branching described above. Unfortunately the specimen 

 was too far advanced to show exactly how this division of 

 the ligule meristem arose. 



Relationships. 



Areschoug, as noted above, seemed to consider Postelsia 

 palmceformis Eupr. as most nearly related to Eisenia in 

 general appearance, although he mentions especially that the 

 leaves (sporophylls) do not arise by splitting, thus recogniz- 

 ing what the writer considers a fundamental difference 

 between Eisenia and all the Lessonioid genera. The origin 

 of the sporophylls as outgrowths, places the genus among 

 the Alariideae, which the writer established to contain genera 

 {Alaria, Ptej^ygophora, Egregia, Ecldonia, Eisenia^ and 

 Ulopteryx or Undaria) more closely related phylogeneti- 

 cally one to the other than to any of the other mem- 

 bers of the Laminariacese. The fact that the sporophylls 

 originate upon the blade side of the transition-place mer- 

 istem and, when this is divided transversely, are carried 

 up by the progress of the blade meristem, demonstrates that 

 the genus is more nearly related to Ecklonia than to Alaria 

 or Pterygophora. The differences existing between it and 

 Ecklonia have already been considered and seem to the 

 writer to be sufiicient reason for considering it to be the 

 highest development of what may be called the Ecklonioid 

 type. 



