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PROFESSOR ~W. C. WILLIAMSON ON THE ORGANIZATION

these layers, as well as along the fewer lines indicated by the thickened peripheralmargin of each primary disk.

Fig. 46 is another transverse section from the same locality as the last, enlarged 4-Jdiameters. It is peculiar inasmuch as it is one of the very few examples of a Dadoxylonin which I have seen concentric lines of growth in the woody zone. Two or three ofthese lines are sufficiently distinct. The more peripheral ones are more faintly marked.

There yet remains to be considered some peculiar divergent elements which exist inseveral of the specimens. These are best seen in the transverse sections figs. 44 & 46.In fig. 44, g, g, two narrow vascular bundles arise from near the innermost margin of thewoody cylinder, and move in nearly parallel lines towards the periphery. Fig. 47 repre-sents a portion of the vertical section fig. 45, enlarged fifteen times, but from a partnot represented in the latter figure; we here see, at </, one of the bundles correspondingto those of fig. 44, g, g, intersected almost, though not quite, radially. We here discoverthat the vessels V, bending outwards to form the bundle g, are derived from the inner-most layer of the woody cylinder b. ' This orientation of these small bundles from theinnermost layers of the wood is suggestive of their primary relation to leaves ratherthan to branches. A similar bundle departs from the interior of fig. 43 near g. Fig. 46exhibits two of these pairs of bundles at g,g. This example is valuable, because itdemonstrates, through their angle of divergence, that these bundles do not proceed todistichous peripheral appendages. Fig. 48 is part of a tangential section of the spe-cimen fig. 44, enlarged 15 diameters. It has intersected two of these bundles at rightangles to their direction, and is interesting as demonstrating their perfect twin-likecharacter. The elementary tissues in the two bundles of this section are destroyed bymineralization, but the other examples clearly show that, when preserved, they consistof the ordinary discigerous fibres of the woody zone.

Fig. 49 is part of a tangential section of the ligneous zone of the Coalbrookdale branch, figs. 33-40, enlarged 62 times. The section was made close to the medulla.In fig. 38 we see a number of cells, f, identical with those of the medullary rays, andwhich, like the latter, doubtless constitute outward prolongations of the medulla. Thefibres which are in contact with these cells, whether coming from above or from below,have their regular arrangement disturbed, so as to be cut through by the section; theybecome suddenly deflected, to make way for the cellular rays pursuing their horizontalcourse towards the periphery.

In the specimen, fig. 42,1 find a solitary bundle given off from the inner margin of theligneous zone at g ; and in the vertical section of the same example, fig. 43, there is nearg a bundle, the position and course of which correspond exactly with that seen in fig. 47.I find no traces of these bundles near the outer margins of such sections of large branchesas I possess *.

The question arises, what is the destination of these bundles 1 On making a series ofsections of the large-leaved Araucaria imbricata and of Taxus , I find in their young

* Thk bundle is not distinctly shown in the figure.