427 
Phloem in the Stems of Dicotyledons . IP 
individuals it can be seen that very considerable variation occurs in the 
lowest region of the organ as regards the origin of the bundles below and 
their history and behaviour on being traced upwards. 1 But the essential 
ground-plan of the structure' is the same in both. 
The structure of T, orientalise L. (Figs, i and 3), and T. porrifolius, L., 
is essentially the same. In the latter plant the arc-shaped internal-phloem 
strands, of the higher part of the stem, each closely adpressed around the 
sclerotic sheath of a bundle of the vascular ring, and giving the bundle its 
‘ bicollateral ’ character, pass upwards into the^capitulum and go to form 
part of the normal phloem belonging to the bundles of the individual florets. 
But some of the medullary phloem-strands die out in situ before reaching 
the inflorescence. 
Leaf. 
The leaf in this genus is rather reduced and grass-like. Hence we 
should expect a corresponding condition of the vascular system. This 
consists of a curved row or arc of alternately larger and smaller bundles. 
In T. pratensis internal-phloem strands are completely absent, at least in all 
leaves examined by the writer. 
In T. orientalis internal-phloem strands occur throughout the typical 
portion of the stalk of the radical leaf on the ventral side of the five larger 
median bundles of the row, but are absent from the smaller lateral bundles. 
One to three strands occur opposite each bundle. The internal-phloem 
strands die out completely in situ in the basal sheathing portion of the leaf, 
so that in the extreme base of the leaf they are absent. They also die out 
above in the midrib of the lamina. 
In T. porrifolius the three or four median bundles of the row, about 
half an inch or more above the base, have each several small strands of 
internal phloem arranged in an arc either closely contiguous to the bundle 
or separated therefrom by two or three layers of cells ; the lateral bundles 
are devoid of them. The internal-phloem strands die out below, and the 
bundles in the leaf-base are entirely without them. 
Hence it will be seen that the internal-phloem strands of the stem in 
this genus have no connexion whatever with those of the leaf, though they 
are doubtless entirely homologous, and, in the writer’s opinion, will have 
been ancestrally directly continuous, therewith. 
Scorzonera. 
Stem . 
This plant is very closely allied to Tragopogon. In conformity here- 
with the character of the medullary bundle-system is extremely similar. 
The same individual variations obtain as in that genus. For example, in 
1 In the higher aerial internodes and in the peduncle the structure of both stems is almost 
identical. In the stem-base of other species a strand may arise de novo in the centre of the pith. 
