U12 MR A. C. SEWARD AND MB A. W. HILL ON THE 



mately parallel to the surface of the primary wood. After becoming free it soon bends 

 outwards almost at a right angle, and passes in a horizontal direction through a broad 

 medullary ray until it reaches the limits of the secondary wood ; at this point it again 

 ascends, bending up abruptly and appearing in transverse section just beyond the outer- 

 most secondary tracheids (PL II. fig. 15 It and PI. III. 16 and 19).* The projecting 

 ridges of smaller tracheids at the periphery of the primary xylem form a reticulum on 

 the corona as seen in surface-view, and, as Bertrand has shown in L. Harcourtii, the leaf- 

 traces appear to be given off from the lower angle of the meshes. A comparison of 

 the Dalmeny stem with the drawings in Bertrand's monograph leads us to consider the 

 mode of attachment of the leaf-traces to the stele identical in the two cases. Each leaf- 

 trace consists of a few primary elongated tracheids, accompanied by numerous thinner 

 walled and shorter spiral and reticulately thickened elements ; these latter elements are 

 shown in fig. 24 in contact with the central projecting leaf-trace group. When seen in 

 a tangential section of the secondary wood, the thicker and larger tracheids of the trace 

 are recognised as a distinct group (PL I. fig. 7 and PL IV. fig. 30) surrounded by the 

 smaller and more delicate elements which exhibit a more or less regular radiating arrange- 

 ment. As seen beyond the limits of the secondary wood, a leaf-trace presents a charac- 

 teristic diploxyloid structure, which on examination reveals certain points of particular 

 interest. There is the well-defined group of long tracheids with the narrowest elements 

 towards the exterior, but not on the edge of the primary elements, and now the radial dis- 

 position of the smaller elements, less distinctly shown in the tangential sections previously 

 referred to (PL I. fig. 7, PL IV. fig. 30), is very striking (PL II. fig. 15, PL III. figs. 16 and 

 17). The smallest and somewhat crushed primary elements occupy a position near the 

 ■outer edge of the primary xylem, the leaf-trace bundle may therefore be described as mesarch 

 (PL III. fig. 19 px). We have in each leaf-trace a group of primary tracheids partially 

 •enclosed by radially disposed rows of secondary tracheids, the latter being characterised 

 by their smaller size and somewhat more delicate structure. The secondary xylem of 

 -each leaf-trace has usually the form of a fan, attached to the sides and outer edge of the 

 primary xylem, but the fan-shaped secondary tissue may extend over almost the whole 

 surface, as seen in PL III. fig. 16. The secondary thickening of the leaf-trace bundles 

 is effected to some extent during their passage through the secondary wood of the stem, 

 and further additions are made to the trace after it has passed beyond the limits of the 

 wood of the stem. This latter point is illustrated by figs. 16 and 19, PL III. m, where 

 the external secondary tracheids of the leaf-bundle pass gradually into thin-walled short 

 meristematic cells. In PL III. fig. 21 a leaf-trace is seen in radial longitudinal section ; 

 the limit of the secondary wood of the stem is slightly to the right of c ; at a we have 

 some of the longer and thicker primary tracheids, and at 6 a broad band of the shorter 

 and thinner secondary tracheids. A portion of the same section is more highly mag- 

 nified in PL IV. fig. 28 ; a and b mark the position of the primary and secondary 

 "tracheids respectively. A tangential view of the secondary elements (fig. 21 b) is 



* Cf. Markfeldt (85), fig. 3. 



