xxx] 



MEDULLOSA 



107 



Superficially the anatomical structure is similar to that of 

 the petioles of Angiopteris or Marattia, and both Williamson 1 and 

 Kenault placed Myeloxylon in the Ferns ; but the collateral form 

 of the vascular bundles, the position of the protoxylem, and the 

 arrangement of the hypoderm tissues, are cycadean features. 



Myeloxylon radiatum (Renault). 



This type is characterised by the radially elongated stereome 

 of the hypoderm. Prof. Zeiller 2 , who has given a very clear and 



FIG. 420. A, B, Myeloxylon radiatum ; A, petiole f nat. size ; B, vascular bundle. 

 C, Myeloxylon sp. vascular bundle; px, protoxylem. D f Medullosa anglica; 

 section of pinnule. (A, B, after Zeiller; D, after Scott.) 



concise description of Myeloxylon, is disposed to regard Cotta's 



Medullosa elegans as a specifically distinct form on the ground 



that there are two concentric zones of stereome in the hypoderm ; 



1 Williamson (76) B. p. 8. 2 Zeiller (90) B. 



