A Monograph of the Genus Alarl i. ]_9 



around the marginal swellings. The relative thickness of the 

 medulla, perimedullary tissue, and the medullary sheath, and the 

 compactness or looseness of the cells of these tissues, show great 

 variation according to the species. 



From the outer limits of the marginal swellings of the medulla, 

 the mednllary tissue runs directly to the blade. Hence, the blade- 

 medullae in both semiblades are practically continuous, with the 

 midrib-medulla interposed at the middle. The cortical tissue of the 

 midrib, however, is sharply divided from that of the blade by a 

 special tissue intervening between them. This tissue is composed 

 of thick-walled, small cells, and compactly fills up the spaces which 

 lie between the outer parts of the marginal swelhngs of the 

 medulla and the epidermal layers at the outer margins of the 

 midrib. The term " spanning cortex " is applied to this tissue in 

 the descriptive part of the species (Plate XVIII, fig. 14, /.•). 



Wille ^) gives in detail structural accounts of the midrib of 

 Alaria esculenta Grev. His description agrees in essential points 

 with the observations stated above. What he calls " Assimilations- 

 System " corresponds to the epidermis in the present Monograph, 

 " das mechanische System " to the cortex, and the " Leitungs- 

 system " to the medulla and the perimedullary tissue taken* to- 

 gether. 



The midrib of A. ßstulosa'^) displays various peculiarities in its 

 external appearance as well as in the internal structure. Its axial 

 part becomes intermittently hollow inside, and is elevated on botli 

 surfaces so as to answer the cavities or bores. The outer edges 

 of the midrib are not rounded or slant but sharply angulatod, 

 already at the early stage of development of the frond, and get 



1) Wille : Beitrage zur physiol. Anatomie der I^iminariiiceen, p. 21. 



2) For a fnllar account on the midrib of Alaria fiatulosa, see, Kibbb : So:ne Points in the 

 Structure of Alaria fUsMosa. (Puget. Sound Mar. Station Publications, Vol I, No. 8. 1!)I"). 



