606 Worsdell. — A natomy of Stem of Macrozamia 
If transverse sections are made of the pith at the periphery, 
where it borders on the vascular zone, here and there one 
of the smaller branches of these medullary bundles may be 
seen running out, accompanied by its mucilage-canal, through 
a medullary ray between the segments of the wood. Its 
xylem and phloem join on in passing to that of the normal 
ring, while the mucilage-canal passes outward to the cortex 
to form a connexion with a similar system of secretory tissue 
in that part of the stem (Fig. 4). 
In connexion with the xylem of the bundles, especially the 
larger ones, there is also very often to be seen what may 
be called a kind of transfusion-tissue, consisting of small, 
angular, isodiametric tracheides with bordered pits, running 
out alone into the tissue of the pith. These are usually 
connected with the first-formed elements of the bundles. 
The proof that the medullary bundles of this plant, as in 
Encephalartos , form a separate cauline system of the stem, 
and are in no wise connected, as in Stangeria and others, with 
the conducting tissue of the peduncles, lies in their origin. 
In transverse sections of the pith, taken from a region not 
far from the apex, mucilage-canals were seen in abundance, 
but no bundles whatever in connexion with them. A little 
further down, however, there began to be signs of a distinct 
differentiation amongst the cells immediately adjoining the 
mucilage-canal, and more especially on one side of the latter. 
The cells were much smaller and, therefore, more numerous. 
Still further down there appeared a difference in the cell- 
walls, especially in those of the outermost of these small 
cells, which gradually became thickened and lignified, these 
elements being evidently on the way to become tracheides ; 
at the same time the innermost cells became further divided 
up as a preparation for phloem-formation. Eventually, the 
primary xylem and phloem became fully differentiated, each 
having respectively the orientation above described for the 
mature bundles (Figs. 6-8). 
Anything of the nature of protoxylem is absent from these 
bundles, as one would naturally expect in secondary structures. 
