XXXJ MEDXILLOSA 105 



cortex R and portions of leaf-bases / — IV. The lowest section, 

 C, shows part of a peripheral snake-ring with a slight swelling at 

 / on its inner side which, as seen in sections B and A, foreshadows 

 the separation of the star-ring S and the consequent break in 

 the continuity of the snake-ring {d, e, sect. B). In section A 

 the gap is closed: in the longitudinal section between B and A 

 the star-ring S is seen to form two branches, a and b, the branch 

 o closing the gap between d and e in section B. These sections 

 demonstrate the formation of a star-ring from the main peripheral 

 stele and the formation of additional star-rings by branching. 



Numerous vascular bundles destined for the leaves are scat- 

 tered in the cortex. The course of the decurrent leaf-base I is 

 shown on the longitudinal faces, its boundary being marked by 

 crowded stereome strands (of the Myeloxylon Landriotii type) ; 

 other leaf-bases are represented by II, III, and IV. 



In habit Medullosa Leuckarti differs from such a type as M. 

 stellata in its relatively shorter and stouter stem and in the shorter 

 internodes. 



Leaves and Eepeoductive Organs. 



i. Leaves. It has already been stated that in some cases 

 petioles occur in organic connexion with Medullosan stems, 

 notably in M. anglica and M. Leuckarti: in the exceptionally 

 rich collection in the Chemnitz Museum, which forms a fitting 

 memorial of the work of the late Prof. Sterzel, there is a stem 

 of M. Leuckarti bearing large petioles of the type known as 

 Myeloxylon radiatum. The occurrence of vascular bundles in 

 the cortex of other species of stenp. identical with those in the 

 attached petioles points to a uniform type of leaf -structure so far 

 as regards the petioles and rachises of Medullosa. While it is 

 clearly imnecessary to distinguish by a special generic title the 

 petrified portions of fronds known to belong to certain species 

 of stems, the frequent occurrence of detached petioles necessitates 

 some distinctive term. The name employed is Myeloxylon: the 

 genus was instituted by Brongniart in 1849 for Cotta's species 

 Medullosa elegans the petiolar nature of which was suspected by 

 Binney in 1872. 



