14 DR. J. D. HOOKER ON WELWITSCHIA. 
Each of the bundles forming the stratum consists of the same elements as those seen 
in the leaf (Plate XIV. figs. 1, 2, 3); but whereas in the leaf they increase only at the base, 
and give off no branches, in the stock their component elements are continually added 
to, and they give off bundles upwards to the crown and downwards to the stock. They 
increase, in short, from mere oblong dots, represented in fig. 6, to the linear bundles seen 
in fig. 2. 
The plexus of the central portion, on the other hand, gives off to the root vascular 
bundles, which, unlike those of the crown and stock, coalesce into indefinite wedges 
(Plate XI. figs. 8 & 9). 
The ascending vascular bundles which run to the ridges of the crown, and some of 
which enter the peduncles, are given off in vast abundance from all parts of the vascular 
stratum. These are very slender, isolated, but crowded, and in a transverse section of 
the crown, above the stratum (Plate XI. fig. 4, lower left-hand quadrant), appear to 
run in not very defined concentric lines, answering to the ridges of the crown. Many 
enter each peduncle, but without manifest order, though after entering they arrange 
themselves in groups having a relation to the bracts, as hereafter to be described. 
The direction of the descending fibro-vascular bundles varies much more than that 
of the ascending, owing to their having to conform to the requirements, both of the 
stock, in which the increase of tissue is mainly centrifugal, and of the root, in which it 
is vertical; and, further, owing to the previously described concavity of this stratum, 
the outer series of these bundles actually ascends instead of descending. To explain 
this, it is necessary to refer to Plate XI. fig.1. Commencing with the last-formed bundles 
in the stock : these start from the vascular stratum Just beneath the base of the leaf, arch 
outwards and upwards, and, running parallel with and near to the floor of the groove, lose 
themselves in the cambium of the periphery. Those which are given off from points 
successively further from the leaf-base follow first a similar course, but successively arch 
downwards instead of upwards, till the innermost of all, which reach the periphery of 
the tumid base of the stock, run parallel to its periderm. All these bundles in the stock 
are usually very slender ; they neither anastomose nor collect into bundles nor wedges, 
except sometimes along the medial line between the lobes of the crown (Plate XI. fig. 3), 
where the bundles from the contiguous leaf-bases become extremely confused, tortuous, 
and anastomose, forming very irregular, ill-defined plates. In old specimens, however, 
many deviations occur. 
Those bundles which descend from the central part of the stratum, through the 
axis of the stock, and traverse the root, are more or less collected into several irre- 
gularly concentric series of wood-wedges, surrounding one or two medullary centres, 
and are separated by wide and interrupted medullary rays and very broad parenchy- 
matous rings. The parenchyma of the axis and root is further traversed by many 
isolated bundles, scattered between the wood-wedges (Plate XI. figs. 8,9; Plate XIII. 
fig. 12). : 
The wood-wedges are collected into groups of 3 to 6 or more, which are parallel to one 
another, but often placed obliquely to the radius and to other groups. Those nearest 
