410 Scott & Sargant. — On the Development of 
circle within them. The lateral bundles of the plumule are 
merely procambial strands, but the third is the direct con- 
tinuation of the midrib from the first leaf, and its xylem is 
partially lignified. This bundle we will call A to distinguish 
it from the others, numbering the cotyledonary traces as in 
Fig. 14. 
As we move downwards through the first internode, the 
cotyledonary traces turn inwards, and at the same time 1 
approaches 2 and 5 approaches 4. Near the base of the 
internode the plumular bundles spread slightly outwards 
until a section is reached in which all the bundles of the 
internode lie on the circumference of a single circle. They 
do not long remain separate from each other. The bundle A 
forks, one bundle fusing with its right-hand neighbour (5), 
and the other with that on its left hand (1). The two lateral 
strands of the plumule fuse with 2 and 4 respectively. We 
have thus five bundles left, corresponding in position with 
the five cotyledonary traces. 
Up to this time all the bundles in the axis have been of 
the stem-type, the phloem-groups lying outside the xylem 
and on the same radius. The xylem itself is centrifugal ; that 
is, the protoxylem is internal. But already the transition 
to a root-structure has begun. The bundles, which now lie 
close to each other near the centre of the section, have 
gradually assumed the characteristic appearance shown in 
Fig. 15. The four lateral bundles form a crescent in front 
of the midrib. The xylem of the midrib is here, as else- 
where, perfectly distinct from the other xylem-groups. These 
features, as we have seen, are characteristic of every young 
node. But the phloem of the midrib ( ph ) is clearly branching 
to right and left, and will ultimately join two phloem-groups 
already partly formed near the horns of the xylem-crescent. 
A third phloem-group is indicated at the place marked * on 
Fig. 15, and it will divide the xylem-crescent into two parts. 
All the phloem of the central cylinder will finally divide 
itself among these three groups, leaving none external to the 
xylem. In this way the alternate arrangement of xylem and 
