458 Stiles . — The Podocarpeae . 
chymatous hypodermal layer on both sides of the leaf. It is occasionally 
interrupted, and always so at the stomata. 
The palisade layer under the upper hypoderm is well marked ; it 
consists of a single layer of cells occasionally doubled. The rather compact 
‘ spongy ’ tissue is about eight layers of cells thick ; solitary stone cells are 
scattered in it. A small resin canal is present under each bundle. Accessory 
transfusion tissue is absent (Text-fig. 2 ,c). 
A remarkable character presents itself at the base of the leaf in this 
species. It has already been stated that the leaf- trace consists of three 
bundles. Shortly after leaving the central cylinder of the stem a cambium 
forms, not only between the xylem and phloem, but also on the upper side 
(as regards the leaf) of the bundle as well. In this way concentric bundles 
are produced which consist on one side of secondary tissue only (PI. XLVII, 
Fig. 21). This state of affairs recalls that found in some of the vascular 
bundles of the axes of the inflorescences of Wehvitsckia, except that, whereas 
in P. nagi the xylem surrounds a parenchymatous area and is surrounded 
by phloem, in Welwitschia the concentric bundles have an amphivasal 
structure, with xylem surrounding the phloem . 1 
vi. Roots. 
An exhaustive account of the structure of the roots of the Coniferales 
is in process of publication by Noelle ; of this account at the time of writing 
only the first part dealing with the Pinaceae had appeared . 2 In the 
description of Podocarpean roots to be given here it is not intended to 
describe these structures in any great detail, but merely briefly to indicate 
the more important characteristics of the roots of the few species available 
to the writer. 
Perhaps the most conspicuous external character of the roots of Podo - 
carpus and Dacrydium is the presence of numerous tubercles, which are 
said to be caused by an ectotropic mycorrhiza. These tubercles have been 
mentioned by Van Tieghem 3 and described by Shibata . 4 
In all the species examined, Dacrydium Franklini , Podocarpus macro - 
phyllus , P. cupressinus , and P. alpinus , the primary xylem forms a rather 
narrow diarch plate. In this respect it agrees with the roots of the Arau- 
carieae , 5 and most of the Abietineae . 6 In some of the latter, namely, 
1 See, for example, Sykes (TO), pp. 192, 202. It is perhaps worthy of note in this connexion 
that Seward and Ford (’ 06 , p. 338) record the presence of such a concentric leaf-trace bundle 
as I have described, in the cortex of a young stem of Araucaria imbricata. Seward and Ford, 
however, ‘ prefer to regard this concentric strand as a leaf-trace of unusual structure rather than 
attribute to what is undoubtedly an exceptional occurrence any morphological significance.’ 
2 Noelle (TO), p. 169. 3 Van Tieghem ( 70 ), p. 195. 
4 Shibata (’02), p. 644. 
6 Seward and Ford (’ 06 ), pp. 343, 345 ; Noelle (TO), p. 170. 
6 Noelle (TO), p. 1 78. 
