428 Worsdell. — Origin and Meaning of Medullary 
one specimen of S. Hispanic a, L., all the medullary strands, when traced 
downwards, die out in situ in the extreme® base of the stem, while in another 
specimen they all pass into the vascular ring. In one individual the 
medullary strands are complete vascular bundles throughout the axis of the 
plant, in another vascular bundles and phloem-strands occur together. 
A mode of origin of the medullary strands was observed in this plant which 
was not described for Tragopogon } In 5. hispanica the vascular ring of 
a vegetative branch was traced downwards to its complete union with that 
of the main stem. As this took place the medullary strands of the branch 
pass into the pith of the stem, fusing up there to form a few large strands. 
Also a bundle from the middle of the abaxial portion of the vascular ring of 
the branch passes into the same region of the pith of the stem, its place in the 
branch-ring being filled by the incoming median leaf-trace bundle. Where 
the incoming branch is a peduncle , most of the inverted medullary bundles, 
occurring in juxtaposition to the bundles of the ring, do not change their 
position as these last pass inwards to form part of the vascular ring of the 
stem. Both in this species and in S. purpurea, L., minute phloem-strands 
may arise, either from the vascular ring at the point of junction of the two 
axes, or de novo , and form a rudimentary central medullary system of the 
branch. In vS. purpurea it was noted that the slenderer branches of the stem 
have no medullary strands, but at their nodes a medullary bundle may 
appear in the bay caused by the exit of the cylinder of a secondary branch. 
In a fairly strong leafy lateral peduncle medullary bundles occur in the 
first two or three internodes, but completely die out above. 
Leaf. 
In S. hispanica there is the same structure as in Tragopogon , with 
internal-phloem strands which die out below. But on the adaxial side of 
the pith there are a few small bundles, devoid of internal phloem, each 
situated at a different radial distance from the leaf-centre, in a portion of 
tissue projecting into the large lacuna. These bundles probably represent 
a remnant of the ventral portion of the erstwhile existing vascular ring of 
the leaf, and are an indication that this organ, which has the same external 
conformation as in Tragopogon , has been reduced in size. 
In S. purpurea the internal phloem behaves in the same way. But it 
was noted, in the case of one node in the stem, that while the median bundle 
of the dorsal row of the leaf was traversing the cortex three minute internal- 
phloem strands arose de novo on its ventral side ; immediately before the 
bundle passes into the vascular ring of the stem the internal-phloem strands 
unite with the ordinary external phloem of the stem.’ 
1 Essentially the same thing was, however, observed in T. pralensis . 
