elements and beyond them a band of radially elongated cells that may be ‘periderm’: still farther out there are some imperfectly preserved vascular bundles that are leaf-traces. This species is important as affording a complete demonstration of the organic connexion between the stem and petioles of the _Myeloxylon Landrioti_ type which indicate that the fronds were probably Alethopteroid. [Illustration: Fig. 418. A, _Myeloxylon radiatum_, part of petiole. B, _Medullosa stellata_; star-ring; × 14. C, D, _Medullosa Leuckarti_; C, primary xylem; D, part of primary stelar tissues and secondary xylem and phloem; × 6. (A–D, Kidston Coll., 1014, 1307, 1238.)] The specimen on which the diagrammatic drawing reproduced in fig. 419 is based has been investigated by Weber and Sterzel[277] and by Solms-Laubach[278]. The figure is a slightly simplified version of that given by Weber and Sterzel; it represents the stem of _Medullosa Leuckarti_ as a transparent object, the two lower transverse sections, B and C, being seen in perspective through the longitudinal faces. The steles are shaded obliquely in the longitudinal sections, and in the three transverse sections, A, B, C, the primary xylem (partial pith) is black and the enclosing secondary vascular tissue radially shaded. The whole block is 9 cm. in length and 6 cm. broad. Only a part of the axial region is shown internal to the peripheral snake-rings and in it are the star-rings _S_, _S_, _b_, and _c_. Outside the main steles is the narrow cortex _R_ and portions of leaf-bases _I–IV_. The lowest section, C, shows part of a peripheral snake-ring with a slight swelling at _f_ 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 _a_ 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. [Illustration: Fig. 419. _Medullosa Leuckarti._ Diagrammatic sketch of stem showing longitudinal and transverse sections: for explanation see text. (After Weber and Sterzel.)] Numerous vascular bundles destined for the leaves are scattered 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 Landrioti_ 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 Reproductive Organs.+