433 
the Adventitious Leaves of Cyclamen. 
Comparison with the preceding figure, however, makes it clear that the 
narrow cells of Fig. 4 are also shallow, and belong to a bundle of rod-shaped 
cells, traversing the original large parenchyma-cell from which they have 
been cut out. 
The procambial tissue supplying a single leaf-rudiment becomes 
connected with two (Fig. 2) or sometimes with three bundles of the 
vascular ring, and somewhat later develops into vascular tissue. The 
elements of the latter are short, their length being usually about the same 
as the diameter of the cells from which they were originally cut out. The 
phloem-elements remain narrow, but the xylem consists of vessels and 
tracheides of greater diameter, the segments or elements being often rather 
broad in proportion to their length, and occasionally isodiametric. 
One case was noted in which a leaf-trace had not completed its xylem 
connexion with the vascular ring, vessels being present only for a certain 
Fig. 2. Fig. 3. Fig. 4. 
Figs. 2-4. 2. Portion of transverse section of tuber, showing procambial trace of young adventi- 
tious leaf. Some parts of the trace are missing, being outside the thickness of the section. x 20. 
3. Transversely cut procambial strand of trace of adventitious leaf. X 260. 4. Longitudinal section through a 
portion of a similar trace, x 260. 
distance from the leaf-rudiment towards the stele. The differentiation of 
the xylem of the leaf-trace may therefore begin al^ the periphery of the 
tuber and proceed inwards, or perhaps it may commonly begin simulta- 
neously along the whole course of the trace, the instance noted above being 
an exception. 
A vascular connexion between leaf and stele is shown somewhat 
diagrammatically in Fig. 5. Some portions of the leaf-trace are missing, 
though a rather thick section was used so as to include the greater part 
of the connexion. The leaf-trace may exhibit considerable irregularities, 
including division into two or more strands, and re-fusion of these, during 
its course, but, speaking generally, it passes inwards in relation to a radial 
plane and with a slightly downward inclination. 
The vessels and tracheides of the leaf-trace usually show either 
reticulate thickening or scalariform or ordinary pitting, only a few cases in 
Gg 
