424 Worsdell. — Origin and Meaning of Medullary 
tion, a continuation of that undertaken for the Cucurbitaceae, is to discover 
the meaning and origin of these internal-phloem strands. 
The method adopted has been to make transverse sections, successive 
and continuous where necessary, from the extreme base of the stem upwards 
to, and including, the peduncle. The nature, position, and course of the 
internal strands were thus studied in all parts of the axis ; upper and lower, 
node and internode. 
The general course and origin of the medullary strands, as seen in the 
lower region of the stem, and which is typical of the genus as a whole, is 
shown in Fig. 2., representing a median radial section . 1 
Stem 1. 
Like nearly all plants of this order, the primary bundles composing the 
vascular ring are strongly individualized and more or less irregular in their 
alinement, as seen in transverse section. There is a wide pith which at 
certain levels becomes in part lacunar. 
In the extreme base of the stem, at, or just below, the ground-level, and 
below that of the insertion of the lowest leaves, viz. immediately above 
where root-structure ends and a pith makes its appearance, two or three 
vascular bundles pass into the centre Off the pith from the vascular ring. Of 
these bundles, one rejoins the ring at a slightly higher level, while the two 
others die out, i.e. end blindly in situ. Before one of them has died qut, 
a few large bundles pass into the periphery of the pith from the ring, where 
they branch and anastomose and, at a rather higher level, give rise to 
a number of bundles in the pith-centre. Where all this occurs is the region 
of the lower crowded leaf-nodes. Higher n,p, these bundles constituting the 
central system die out in situ. But before they have all died out a new 
system of peripheral bundles arises close to the vascular ring ; these 
bundles arise de novo, i.e. in the pith without any relation to the ring. At 
first consisting of phloem only, they soon acquire a considerable amount of 
xylem nearly all round the phloem. At a higher level some of the largest 
of these bundles join the ring. Slightly higher still, great numbers of tiny 
phloem-strands arise de novo in the central region of the pith and, a little 
higher up, the peripheral bundles above cited dwindle in size, and, together 
with the central small strands, form a single system of medullary strands 
throughout the pith. The smaller strands, consisting of phloem only, occur 
everywhere, even in the embouchement of the rays in the vascular ring. 
Tracing the structure still higher, the central strands and the smaller of those 
at the periphery decrease greatly in number, until only a few remain over 
in the central region ; at the same time the larger peripheral strands give 
1 All the figures illustrating this paper are diagrammatically drawn. The parts shown black 
represent xylem, the dotted areas represent phloem. 
