XLIV] 



BLECHNUM 



165 



development shows that the indusium-Hke margin is constant throughout 

 the extended genus Blechiiiun, and it will here be regarded as the "phyletic 

 margin." This, however, comes to be apparently intra-marginal in Eii- 

 Bledinuvi, owing to the formation of a new structure which originates alone 



Fig. 687. Tip of a pinna of Blechmini orientale L., made transparent so as to 

 show the relation of the coenosorus on either side of the mid-rib to the vena- 

 tion of the blade. Each coenosorus is protected by a continuous "indusium" 

 which is phyletically the leaf-margin : the expanded leaf-surface on either side 

 is a new formation, the " flange," by means of which the area of photo-synthesis 

 is increased. This is a typical Eu-Blechnum. ( x 3.) 



the line of greatest curvature: this will here be called the "flange." Its 

 origin has been traced by comparison of numerous species: but though the 

 flange may produce a large photo-synthetic expanse in Eu-Blechnum, the 

 position of the phyletic margin is not thereby altered. Its identity is 



Fig. 688. ^ = diagrammatic section of the fertile pinna of the type, 

 Lomaria, with incurved margins, but no flange. B — 2, similar section 

 of the type, Eii-Blechnum, showing the same parts as before with the 

 addition of flanges right and left. Compare Fig. 687. 



maintained throughout, and it corresponds to the incurved margin of the 

 fertile pinna in Matteuccia. The relative position of the parts is best seen in 

 sections (Fig. 688, A, B), from which it appears that no membranous 

 indusium, such as that seen in Onoclea or in M. struthiopteris, is present 

 either in Lomaria or in Ett-Blechmim. It has been seen in the preceding 

 Chapter that M. intermedia has no indusium: this species thus supplies the 



