Two Palaeozoic Stems from India. 3 1 7 
fossil, and here there is no indication that the two traces ever joined. 
In other words, there is always a distinct intercalary bundle, as in Ephedra 1 
or any of the living Angiosperms, 
Various stages in the exit of the leaf-traces are shown in the photo- 
micrographs. Fig. 7, PI. XVIII, represents three bundles ; the two outer 
ones are foliar and have commenced their journey towards the exterior, but 
are still pursuing a longitudinal course ; in Fig. 8 they have become bent 
so that a transverse section of the stem cuts them almost longitudinally ; 
Fig. 9, a tangential section of the stem, shows the traces still farther sepa- 
rated. On one occasion a trace was seen to divide as it passed out through 
the wood; it is represented in Fig. 12. A somewhat similar case was 
described by Dr. Scott in the case of M. platypodium , 2 where the proto- 
xylem of the strand divided while still in the wood. 
Primary Wood. 
In describing the structure of the wood, it will be simplest to start with 
the internode. As is shown in Fig. 2, PI. XVII, the primary tissue is 
localized in bundles, of which there are 40 to 50 scattered around the circum- 
ference of the pith. All seem approximately the same size, without apparent 
differentiation into cauline and foliar. In transverse section there is no 
distinction between primary and secondary xylem, the elements being 
radially arranged throughout. Longitudinal sections, however, show that 
the protoxylem is strictly endarch and situated at the apex and along each 
side of the xylem wedges. Thus tangential sections of the bundle (Fig. 17, 
PI. XIX) show the larger spiral and reticulate metaxylem cells bounded on 
each side by the smaller lumened, often crushed, protoxylem — the whole 
enclosed on its inner face by the transfusional sheath described above. In 
radial section the centrifugal development of the bundle is even clearer 
(Fig. 6, PI. XVII) ; at the extreme left is the sheath, its cells becoming 
longer and narrower towards the wood ; next comes the protoxylem, and 
then the metaxylem, which through a transitional zone of from 15 to 20 
spiral and reticulate elements grades into the typical pitted tracheides of 
the secondary xylem. This arrangement holds for the bundles themselves, 
but in the interfascicular regions, as in Mesoxylon , the secondary wood 
abuts directly on the pith (Figs. 3 and 4). In the extensive transitional 
zone between primary and secondary wood proper, this Indian fossil resem- 
bles Cordaites , Mesoxylon , Poroxylon , &c., but it differs from them all in 
the absence of centripetal wood. 
We now come to the nodal region, and here conditions are somewhat 
complicated by the greater development of primary tissue. Instead of 
being limited to a few elements on the inner margin of the wood, there are 
distinct groups of primary elements at the apices of the xylem wedges. 
1 Thompson (1912). 2 Scott and Maslen (1910). 
