A Monograph of the Genus Alaria. 7 



The cylindrical cells in the perimedullaiy tissue and the cells 

 of the cortex have nnmerons pits in their cell-walls. They are 

 septated by thin middle-lamellae so as to hinder the free passage 

 of cell-contents. Their abundant presence in the cell-walls gives 

 a very irregular appearance to the forms of the cell-lumens, espe- 

 cially when the latter are as narrow as in the cortical part. A 

 simüar structure has been excellently illustrated by Wille i) for 

 the cortical part (" mechanische Gewebe ") of Alaria esciilenta, 

 Grev., and by McMillan 2) for that of the Pterygophora stipe. 



The cortex and the epidermal layer appear as continuous, 

 more or less regular, radiating lines. The latter may be distin- 

 guished from the former by having cells of thinner membrane and 

 greater diameter and by the chromoplasts. The limitation of the 

 two parts is not sharp in the first-year fronds, but is sudden and 

 well-marked, together with an annual ring, in the second-year 

 fronds (Plate XYIII, fig. 12). 



Wille ^) also distinguishes four concentric zones in the struc- 

 ture of the stipe of Alaria esculenta of " wenigstens vier Jahre 

 alten Exemplaren." His " Zone 1 " corresponds to the epidermal 

 layer, " Zone 2 " to the cortex, " Zone 3 " to the perimedullaiy 

 tissue, and " Zone 4 " to the medulla in the above description. 



The mucilage lacunae, very common among Laminar ia, are 

 entirely wanting in the stipe of Alaria. Instead of them there 

 are, at least in an embryonal stage of the frond, the mucilage 

 glands. They are found in the epidermal layer immersed at the 

 depth of a few cells, dispersed without any definite order along 

 the periphery. As the meristematic layer of the cortex lies in a 



1) Wille : Beitrage z. physiolog. Anatom, der Laminariaceen, fig. 14. 



2) McMillan : Observations on Pterygophora, PI. LXII, fig. 6-7. 



3j Wille: Beitrage z. physiolog. Anatom, der Laminariaceen, p. 17. 



