MEDULLOSEAE 437 



dermal zone (hy), consisting of numerous vertical strands 

 of fibres, interspersed with parenchyma, and accom- 

 panied by secretory canals of the usual Cycadean 

 type. 



The whole interior of the leaf-stalk is occupied by 

 a short-celled ground-tissue, containing secretory canals 

 {in.c\ and traversed by the numerous vascular bundles 

 (v.b), ranged more or less regularly in concentric circles. 

 The general structure was, in fact, much like that of 

 the petiole of a recent Cycad. The individual bundles 

 likewise resemble those of the recent family, differing 

 only in the fact that their xylem was entirely centri- 

 petal, while in a modern Cycad a small amount of 

 centrifugal wood is also present. This difference, 

 however, does not seem to have been an absolutely 

 constant one, for in some of the Medulloseae the 

 foliar bundles are described as having precisely the 

 Cycadean structure. 



Petioles of the kind described have long been known 

 under the generic name of Myeloxylon ; the particular 

 form belonging to our Medullosa resembles that named 

 by M. Renault Myeloxylon Landriotii, distinguished 

 chiefly by the multiseriate arrangement and elliptical 

 transverse section of the fibrous hypodermal strands. The 

 same petiolar structure, however, was no doubt common 

 to certain other species of Medullosa. The fact that the 

 fossils named Myeloxylon are nothing but the petioles 

 of Medullosa had previously been proved, by Weber 

 and others, for one of the Continental species. 1 In the 

 case of M. anglica the conclusion is perfectly obvious, 



1 See Weber and Sterzel, Beitrdge 2. Kenntniss der Medulloseae, 

 Chemnitz, 1896. The original discovery was made by Weber, about the 

 year 1880. 



