Duthie . — Anatomy of Gnetum africamim . 599 
found in the axils of these leaves. Sections were also cut through old 
nodes with opposite lateral branches in the axils of the scale leaves. 
Again eight bundles leave the stele as in the cases already described. These 
bundles branch in passing through the cortex, 1 the median leaf-traces 
often bifurcating before the lateral are quite clear of the vascular ring. 
A number of these branches enter the axillary bud, while others pass into the 
leaves. The material available did not admit of all the details of the leaf and 
axillary branch supply being made out, but in the sections examined a brush 
of xylem elements appears to pass up into the free part of each scale leaf. 
Petiole. The short petiole of the foliage leaf is slightly furrowed above 
and convex beneath. Numerous latex tubes and fibres traverse the petiole 
and pass into the midrib. A few lignified spicular cells are also present. 
The four leaf-trace bundles remain distinct through the entire length of the 
petiole. A considerable amount of secondary tissue is formed by the 
cambium of each of these bundles. 
Lamina. The four bundles of the petiole enter the base of the lamina 
and fuse laterally in pairs about one-fourth of the way up the midrib. Com- 
plete fusion occurs at some little distance above this point. The cambium 
of the midrib forms a considerable amount of secondary xylem and phloem. 
As is well known, the reticulate venation of the Gnetum leaf is of the normal 
dicotyledonous type (Figs. 6, 7). The leaf lamina, though fairly thin, is 
extremely tough. Below the cuticularized upper epidermis lies a single 
row of short palisade cells. The many-armed, spongy mesophyll occupies 
a considerable part of the substance of the leaf. The sclerenchymatous 
framework of the lamina consists of branched acicular cells and elongated 
fibres. The former have lignified, finely striated walls, occasionally per- 
forated by simple pits. They are stellately branched and differ from the 
spicular cells of Welwitschia in the absence of an outer crystal-bearing layer 
of cellulose from their walls (PI. LIX, Fig. 29). They occur for the most 
part in the stellate parenchyma close to the lower epidermis, the more 
prominent arms usually lying in the plane of the lamina. The fibres, which 
are far more numerous, are of enormous length. Their cellulose walls are so 
strongly thickened that in places the cell lumen is almost entirely obliterated. 
On isolating these fibres after maceration the ends are frequently found 
to be shortly and unequally branched. Similar branches occasionally 
occur at other points, but are seldom of great length (Figs. 28, 31). A bun- 
dle of these fibres strengthens the leaf margin and prevents tearing. These 
marginal fibres resemble those of the axis in being much straighter than 
the fibres described above and entirely unbranched. 
The ordinary epidermal cells of both surfaces have strongly undulated 
walls (PI. LVIII, Fig. 22), but opposite the larger veins they are narrower and 
more regular in outline. Nodose thickenings of the walls are fairly common. 
1 Strasburger (8). 
R r 2 
