A Monograph of the Genus Alurhi. 133 



of these species seem to lie, as proposed by Strömfelt, in tlie 

 shape of cross section of the midrib. Eupeecht has also taken a 

 similar point as an important character in discussing Fucus tetra- 

 gonus and Fucus teres, comparing them with A. esculenta P. et R. 

 BÖRGESEN too, used this character in distingnishing his Faeröuse 

 specimens into A. esculenta Grev. and A. Pjjlaii Grev. What 

 systematic value the rectangular or ancipituous shape of the cross 

 sections of the midrib may have is very doubtful to me. Börgesen 

 notes that young specimens of A. esculenta " often have a midrib 

 which must most properly be called two-edged." This fact induces 

 me to suppose, as well as the fact that A. flagellar^ is known in 

 a sterile stage only, that the two species described by Strömfelt 

 are really only one species and also that they may be local forms 

 of A. esculenta Grev. It appears almost safe to bring A. linearis 

 Ströme, dow^n to a synonym of A. esculenta Grev. There still 

 remains a question about A. flagellarls. It may be regarded as a 

 younger form of A. cscuhnta Grev., or referrable to A. Pijlail 

 Grev., or a distinct form or species. 



It is to be noted that there are two distinct forms of the 

 cross sections of the midribs of the Atlantic forms of Alaria which 

 are passing under A. esculenta Grev. One is decidedly rectangular 

 and has a well marked spanning cortex and thick medullary 

 sheath, and the cartilaginous content in the sieve cells is highly 

 developed. The other is elliptical or ancipitous elliptical in the 

 shape, the meduUary sheath slightly broader than in the remaining 

 part, the spanning cortex hmited to the crucial point and the 

 cartilaginous content of the trumpet liyphse, so far as I have 

 examined, not recognizable. Experiences teach me that the anatomi- 

 cal differences as here mentioned may not be of much importance 

 in the specific distinctions. Still, these two forms appear to me 



