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W or sdelL- — Origin and Meaning of Medullary 
S. arvensis, L. 
Stem . 
There are medullary phloem-strands at the periphery of the pith, and 
at the nodes they are also scattered throughout the pith. 
Leaf . 
An arc of bundles. The median one has two small internal-phloem 
strands ; these die out just before the bundle enters the stem. 
Crepis. 
C. biennis, L. 
Stem . 
Considerable variation in the development of medullary strands was 
found in this species. In cultivated specimens traces of them were found. 
In wild specimens no trace of them could be discovered. In those cases 
in which they occur it is in the lower portion of the stem, the higher being 
devoid of them. 1 Moreover, they are always found at, or in the near 
neighbourhood of, a node. They arise both de novo and from the vascular 
Figs. 9, 10. Crepis biennis. Segments of vascular ring of stem, showing medullary strands 
(ms) in the bay formed by the outgoing median leaf-bundle (mlb). One of the lateral leaf- 
bundles at lib. x 9. 
ring, as seen in tracing them from below upwards, and they branch and 
anastomose, as is usual in other genera. They occur, either as vascular 
bundles or phloem-strands, always opposite and contiguous to a leaf- and 
branch-trace (Figs. 9 and 10). ‘ Most of them pass out into either a branch- 
or leaf-trace to constitute part of the normal vascular tissue, but others 
were seen to join the cylinder of the stem. The fate of one strand was 
interesting. It arose de novo in the outer part of the bay formed by an 
outgoing branch-cylinder. It first of all branched into two ; each strand 
so arising formed connexions with the branch-cylinder on either side. 
They then passed out, after one of them had again divided into two, with 
the leaf-trace bundle, while the branch-cylinder closed up to the inside of 
1 In another cultivated specimen, from a distinct batch of seedlings, one or two nodes in the 
upper part of the stem exhibited each a well- developed medullary amphivasal bundle. 
