Dr. D. H. Scott. 



Except for the possible absence of secondary wood from the undivided 

 leaf-trace — a doubtful point on which no stress can be laid — there is no 

 difference between the stelar system of M. pusilla and that of M. anglica. 



The Cortex and Leaf-bases. 



In M. pusilla, as in M. anglica, no sharp limit can be drawn between cortex 

 and leaf-base except at a level where the latter is already marked off by an 

 internal barrier of sclerotic strands. The appearance of such a barrier is, of 

 course, a preparation for the departure of the leaf-base from the stem. 



In the transverse sections the best preserved leaf-base is only partly 

 delimited in this way ; a sclerotic band runs inwards from each side, but 

 does not extend right across. Of the two imperfect leaf-bases, one appears 

 to be completely marked off by an internal sclerotic band, while the other is 

 not yet delimited at all (Plate 13, figs. 1 and 2) 



A convenient boundary between cortex and stelar system is provided by 

 the periderm (fig. 3). The cortex, which contains numerous gum-canals, is 

 not very well preserved, but it can be seen that the vascular bundles in this 

 region are, on the whole, larger and rounder in section than those which have 

 definitively entered the leaf-base. 



At one place a group of four or five bundles is shown, which has, to all 

 appearance, arisen from the division of a single primary leaf-trace (text- 

 fig. B). This group lies in the cortex, which is here well defined by the 

 sclerotic band on the exterior and the periderm within. Similar groups of 

 bundles formed by division are well known in the cortex of M. anglica 

 (Scott, '99, Plate 6, Phot. 9; Plate 11, fig. 12). In both species later stages 

 in the division of the bundles are found in the leaf-base itself. 



The well-preserved leaf-base is best shown in the section represented in 

 Plate 13, fig. 2, and is here sufficiently perfect for the bundles to be counted 

 with approximate accuracy. There are 15 peripheral bundles {i.e. on the free 

 side), nine on the side attached to the stem, and eight, of which two are 

 double, in an intermediate position. Thus the interior of the leaf-base is 

 poor in bundles, a condition which also exists in that of M. anglica at a 

 corresponding level (Scott, '99, p. 100). 



The bundles near the periphery have assumed their definitive petiolar 

 character, while the inner bundles more resemble those of the cortex, and 

 are still undergoing division. Some of the former are very well preserved 

 (Plate 13, fig. 4), with the phloem practically perfect ; the usual exarch, 

 collateral structure is obvious. The sectional form of these bundles is often 

 slender, i.e. elongated radially, as also occurs sometimes in M. anglica, 



