87 



III. Khexoxylon africaimm, a new Medullosean Stem. By Nellie Banceoi't, 

 JB.SG.{Lond.), F.L.S., 1851 JResearch Scliolm\ Newnham College^ CamhHdge. 



(Plates 10 & 11.) 



Eead 6th February, 1913 



I. iNTRODrCTION. 



IhE specimen wliicli forms the subject of this paper was sent to Prof. Seward by 

 Dr. A. W. Eogers, the Director of the South African Geological Survey, as an unusual 

 type of petrified stem-structure. The block was sent to Dr. Rofijers without any infor- 

 mation as to its locality or associations, but in his letter in reference to the fossil he 

 writes : — " I have no doubt that the specimen came from the Cape." He adds : " It 



probably came from the Karroo rocks." 



Since the Karroo Series ranges from the Dwyka boulder-beds and shales to the 

 Stormberg Series — i. e., in terms of European geological chronology, from the Upper 

 Carboniferous (approximately) to the Ehgetic or Lower Jurassic (5, pp. 233-243) — the 

 exact age of the specimen must be left in doubt, so far as concerns evidence other than 

 that supplied by the structural features themselves. 



11. Description of the Specimen. 



(a) Ecctei^nal Characters. 



The specimen is silicified, and represents what is evidently a portion of a stem, the 

 outer layers of which are absent. The length of the specimen before cutting was about 

 6-5 cm. and the diameters 7-2 X 57 cm., the structure being somewhat elliptical in 



transverse section (PL 10. fig. 1 ; PI. 11. fig. 8). 



Externally the fossil has an irregularly ribbed appearance, with vertical and alter- 

 nating bands of varying width and of two different textures. The more outstanding 

 bands consist apparently of a fairly porous and loose ground-tissue, while the alternate 

 bands show fine vertical striations and are very compact (PI. 11. fig. 1, a & st). These 

 correspond to the irregular masses of compact texture which are seen on the transverse 

 surface of the stem (PI. 10. fig. 12), and which are evidently vascular structures. 



The cut transverse surface shows general ground-tissue, more compact towards the 

 interior of the stem than at the outer parts, where here and there it is very porous 

 (PI. 11. fif. 8). Embedded in this ground-tissue, mainly at the periphery of the block, 

 are the masses of compact tissue mentioned above. Each of these is presumably a stele 



SECOND series. — BOTANY, VOL. VIII. 



o 



