A Monograph of the Genns Alnrht. 5 



distinguished into three kinds, the epidermal layer, the cortex and 

 the medulla. 



In the cylindrical part of the stipe, the epidermal layer and 

 the cortex form concentric rings when observed in cross sections 

 (Plate XVIII, fig. 12). In the center of the circular section the 

 medulla of a compressed elliptical shape is found. Interposed 

 between the medulla and the cortex there is a zone of distinct 

 structure, sheathing, as it were, the former. It is clearly distin- 

 guished from the two parts by having large cells of irregular 

 arrangement and fibrous colls compactly interposed among them. 

 Within this is the elliptical medulla with its major axis nearly 

 equal to the diameter of the said area. I will call the area 

 " perimedullary tissue " for convenience' sake. This tissue is the 

 main source of the medullary hyphae, agreeing with the similar 

 tissue in the stipes of Laminar ia. The cells are remarkably thick- 

 walled. When stained in a solution of aqueous anilin blue the 

 cell-wall gives a vivid differentiation of blue colour in sharp con- 

 trast to that of the other parts. Similar result has been obtained 

 by Wille 1) by treating the tissue with chloriodide of zinc (Plate 

 XVIII, fig. IG). 



The large, thick-walled cells in the perimedullary tissue must 

 not be confused with the similar ones scattered in the medulla. 

 In the cross sections they appear very much alike. Longitudinal 

 se3tions, however, reveal the fact that the former are cylindrical 

 cells forming continuous filaments of uniform diameter, and that 

 the latter are the swollen parts of the trumpet hyphae. Some of 

 the trumpet hyphae become thick-walled, as has been already 

 observed by Wille 2), and may assume a similar appearance, ni 



1) Wtule: Beitrüge z. physiolog. Anatom, der Laminariaceen, p. 26, fig. 11. 



2) Wnj.E : I. c, fig. 37. 



