358 DR D. H. SCOTT ON THE 



pairs of vascular bundles which pass out, almost horizontally, through the woody zone 

 (Williamson, I.e., fig. 60 ; cf. PI. II. phot. 12 in the present paper). He was at that time 

 inclined to believe that they supplied paired branches of the stem (I.e., p. 517), though 

 in a previous Memoir, in discussing similar structures in other Dadoxylons, he said 

 " either two bundles went to one leaf with a double midrib, or the leaves were arranged 

 in pairs."* On a later occasion, Williamson t compared these paired strands in 

 Dadoxylon with the closely similar double leaf-traces of the recent Ginkgo. There can 

 be no doubt that in the fossil, as in the recent stem, each pair of bundles represents the 

 trace of a single leaf. 



The stem, as preserved, is about 1*8 cm. in diameter ; nothing beyond the secondary 

 wood is shown. The pith, which has a diameter of from 5 to 6 mm., is obtusely 

 pentagonal, the prominent angles evidently corresponding to the points of exit of the 

 paired leaf- trace bundles. At two places in photograph 12, the dark bands, marking 

 the position of a double leaf-trace, are seen passing out from the two sides of a truncated 

 angle of the pith. 



The pith, which is not very well preserved, consists of a fairly uniform paren- 

 chymatous tissue, the cells averaging about '07 mm. in diameter, but becoming smaller 

 towards the periphery. They are for the most part filled with dark, carbonaceous 

 contents ; at some places a larger carbonaceous mass is seen, suggesting the presence of 

 a secretory space, but this appearance may merely be due to disorganisation. 



The secondary wood is very dense, and has typical Dadoxylon characters. The 

 tracheides are narrow, averaging "025 mm. in radial and rather less in tangential 

 diameter. Their radial walls bear multiseriate bordered pits, closely packed. The 

 medullary rays are small, one to eight cells in height, and hardly ever more than one 

 cell thick. In rare cases a ray two cells thick in the middle may be met with. The 

 absolute width of the ray is from •Ol-'OIS mm. Fig. 25 gives a fair idea of the aspect 

 of the wood in tangential section. 



The interest of the specimen lies in the fact that distinct strands of primary xylem 

 occur at the inner margin of the secondary wood, and in contact with it. In one of 

 the transverse sections (No. 1381 in the Williamson Collection) five of these strands 

 are present; the other transverse section (now No. 1504 in my collection) only shows 

 four, the tissues having been destroyed where the fifth would lie. Some of these strands 

 are double, others single. Phot. 1 3 represents a double strand ; the two groups are 

 each about '15 mm. in tangential width, and are separated from each other by a space 

 nearly equal to their diameter. The smallest elements lie towards the middle of each 

 strand. Fig. 24 represents on a larger scale another bundle, in which the two strands 

 are partly fused, the whole having a diameter of about "3 mm. ; the smallest elements 

 are in two groups, accompanied by parenchyma, and no doubt represent the protoxylem. 

 Towards the outer side the irregularly grouped primary tracheides pass over gradually 



* Part VIII., Phil. Trans., 1877, vol. 167, part i. p. 231. 

 t Part XII., Phil. Trans., 1883, pt. ii. p. 469. 



