16 Vol. XLni., Art. 1.— K. Yeiido : 



Yendo and Undaria pinnatlfida Sue. The first species has no true 

 midrib but a thick meridional area, on which the sori hmitedly 

 develop. Okamuea termed the area " fascia." The other two 

 species have the true midrib which remains absolutely sterile. In 

 spite of remarkable morphological differences, he proposes to bring 

 them all under the single genus Undaria, extending its conception. 

 I hold, however, the view that the midrib in the blades of Alaria, 

 Undaria and Hirome should be taken as a special organ of distinct 

 significance. The gradations of the soial localizations of the three 

 species as illustrated by Okamuea may well indicate that they are 

 genetically related to one another, directly or indirectly, but can 

 not have more significance than that, in the modern principle of 

 systematic survey. 



The true midrib has a well-marked structural difference from 

 the laminai part. The most striking point is the longitudinal 

 course of the cortical and the hyphal cells in the former, while 

 they run at largo decussately or patently from the midrib in the 

 latter. In tlie meridional and the extra-meridional area of the 

 blade of Laminaria, they run equally in tlie longitudial direction ; 

 also in Laminaria. Peterseniana and Ptcrygopliora calif ornica. Hence 

 it is quite natural that the fresh blade of Laminaria tear longi- 

 tudinally, but curiously tlie dried ones tear transversely. 



In Acjarum Gmelini the thickened meridional area approaches 

 in structure and in appearance to the true midrib ; and more so 

 in Arjarum Tarneri. In this respect, the midrib of Agarum may 

 be taken as a link showing intermediate characters between the 

 true midrib and the meridional area. 



The typical midrib of Alaria is complanatcd with rounded 

 edges, elevated equally above both surfaces of the blade. The 

 cross sections, therefore, show an elongated elliptical shape with a 



