This species[541] affords a good illustration of the generic characters already summarised. The strap-like leaves are fleshy and the occasionally forked, parallel or slightly divergent, veins are embedded in a homogeneous mesophyll with hypodermal strands of mechanical tissue. The pith consists of parenchyma in vertical series with scattered secretory sacs and differs from that of _Cordaites_ and _Mesoxylon_ in the absence of transverse discs. There are 13 primary-xylem strands close to the inner edge of the secondary wood: the centripetal tracheids are scalariform or have multiseriate pitting like that in the secondary xylem. The structure of the leaf-traces is clearly shown in fig. 464: the double trace seen in fig. 464, C, has two protoxylem-strands accompanied by some parenchyma, and these are almost enveloped by the metaxylem tracheids which abut on the secondary wood. At this stage in its course, that is just before bending outwards, the centripetal xylem reaches its maximum development and the trace forms a prominent and broad twin-strand in striking contrast to the two narrower and tangentially extended strands shown in fig. 464, E, D. Each of these strands with a single protoxylem-group would at a higher level assume the broader and more compact form and contain two protoxylems as in fig. 464, C. The tracheids of the secondary xylem have 4–7 alternate rows of contiguous alternate pits on the radial walls: the medullary rays are 2–3 cells broad and may be 60 cells deep. According to Renault[542] several small oblique pits occur on the radial walls of the ray cells. The secondary phloem, separated by a normal cambium from the xylem, forms a broad band of sieve-tubes with lateral sieve-plates like those in _Medullosa anglica_ alternating with tangential rows of parenchyma. The cortex is relatively narrow and in older stems is chiefly occupied by secondary tissue formed from deep-seated phellogens. [Illustration: Fig. 464. _Poroxylon_. A, B, _Poroxylon Boysseti_. A, transverse section of leaf in the region of lateral expansion of the petiole; B, portion of vascular tissue of A. C–E, _Poroxylon Edwardsii_. C, leaf-trace showing recent separation of the two protoxylems; D, leaf-trace at a lower level with more widely separated protoxylems, _px_; E, leaf-trace intermediate between C and D. (From photographs supplied by Prof. Bertrand.)] _Poroxylon Boysseti_ Renault. The stems of this species agree closely with those of _P. Edwardsii_, the chief difference being in the structure of the secondary phloem which does not show the regular concentric alternation of sieve-tubes and parenchyma. _Poroxylon stephanense_ Bertrand and Renault.