A îlonograph of the Genas A'w'ia. 25 



freshwater and tlien mounted. A. ßstidosa, the largest form of the 

 genus, has the blade enormously thick and practically leather-like 

 while in its fresh state. Bat when mounted for a herbarium 

 specimen in the latter method related above, the blade turns into 

 a thin and brittle papyraceous substance. 



When a dried specimen is sectioned and dipped in water it 

 swells up much more than to its former natural thickness. In 

 such specimens it is rather difhcult to discern the true anotomical 

 character of the frond. A comparison of the details of construc- 

 tion of the blades of different species is therefore beyond my 

 present enterprise. In the present paper the distinctive terms are 

 still used, but very cautiously. 



Jliärib» 



The term midrib as applied to the Laminariaceous frond is 

 sometimes found to be used ambiguously. The thickened area 

 w^hich runs longitudinally in the middle of the blade of Laminaria, 

 Pterygophora and the like, and the sharply defined longitudinal 

 elevation on the blade of AI aria, have been equally called midrib 

 by McMillan.^) Setchell^) previously seems to" have been reluc- 

 tant to adopt this usage since he chose to call the former " a sort 

 of indefinite midrib " and for a similar thickened portion of the 

 blade of Pleurophycus, " midrib " in quotation marks. In my 

 former papers =^) the area is termed " meridional region." 



Quite recently Okamuka^^ published a paper treating of the 

 relationsliip of Laminaria Petcrseniana Kjellm., Hirome undarioiles 



1) McMillan : Observations on Pterygophora, p. 737. 1002. 



2) Setchell: Didtributiou of Laminariaceae, p. 3i7. 1893; and Notes on Algae. I. p. 123. 

 1901. 



3) Ykndo: Development of Costaria, Umlaria and Liminaria, p, 711. 



4) 0K.VMÜE4. : Undaria and its Species, p. 269. 



