20 Vol. XLIII., Art. 1.— K. Yendo : 



markedly prominent as the bores are completed. Plate I, fig. 4 

 will spocik better than description. 



The boring is practically a lysigenetic result, taking place in 

 the axial region of the medulla at the post-embryonal stage of the 

 frond. Disorganized hyphal cells and the residual trumpet cells, 

 often filled with callus, are found on the inner surface of the bores. 

 The medullary tissue is poorly developed near along the bores but 

 markedly thickened at the marginal swellings. The perimedullary 

 tissue is absent along the bores but weh developed in the com- 

 planated regions of the midrib, and terminates at its marginal 

 elevations. The spanning cortex is also to be seen at each marginal 

 elevation of the midrib (Plate I, fig. 4). 



The cortical portion of the midrib of A. fistulosa is composed 

 of irregularly arranged parenchymatic cells. The greater part of 

 the thickness of the bore -wall is occupied by this tissue. 



The shape of the cross section of the midrib has often been 

 used as a distinguishing character of Alaria species. Repeated 

 observations on various species have taught me the danger of 

 adopting sucli a view. As stated before, the midrib is much com- 

 planated with sloping edges while the blade is yet young. When 

 the secondary growth in breadth begins to take place in the blade, 

 its midrib gains the characters of a matured plant. By referring 

 to the figures ni the accompanying plates (Plate XI, XIII, fig. 2-3) 

 the reader will readily understand to what degree tlie cross sec- 

 tions of the midrib of a species may vary. Certain species have 

 of course a peculiarity in tlieir midribs and this peculiarity may 

 be already perceived even in an early stage of development. A. 

 fistulosa can not be mistaken for others by its intermittently 

 hollow midrib. Yet, tlie distinguishing of species of Alaria by 

 more cross sections of the midrib, — at least to put a great im- 



