in the Root and Stem of Dicotyledons. 
299 
EXPLANATION OF FIGURES IN PLATES XVIII, 
XIX, XX. 
Illustrating Messrs. Scott and Brebner’s paper on Internal Phloem. 
The following lettering is used throughout : — 
cb 1 — normal cambium. 
cb 2 — medullary cambium. 
cb 3 -- extrafascicular cambium. 
ph l = normal external phloem. 
/A 2 = medullary phloem. 
ph 3 — phloem-islands, imbedded in the xylem. 
x 1 = primary xylem. 
x 2 = secondary xylem. 
x 3 = centripetal xylem, formed by medullary cambium. 
px = protoxylem. 
pc = pericycle. 
e = endodermis. 
Figs. 1-5, Browallia viscosa. 
The line C-C 1 is the plane of the cotyledons. 
Fig. 1. Transverse section of hypocotyl. Numerous groups of medullary 
phloem. In this and the following figures the xylem of the cotyledonary traces is 
shaded dark, x 300. 
Fig. 2. Do. lower down. Three internal phloem-groups are passing out. 
x 300. 
Fig. 3. Do. still lower. Another phloem-group is seen in the xylem on its 
way out. x 300. 
Fig. 4. Do. near root. Little medullary phloem is left. One group is seen 
passing out. x 300. 
Fig. 5. Transverse section of tap-root, showing typical diarch structure. All 
the phloem is now united in the normal position, x 300. 
Fig. 6. Asclepias obtusifolia. Part of a transverse section from a thickened 
root. Two phloem-islands shown imbedded in the xylem-parenchyma, near a 
group of Vessels, x 150. 
Figs. 7 and 8. Thladiantha dubia. 
Fig. 7. Semi-diagrammatic transverse section of a root to show the distribution 
of the tissues. The protoxylem-groups coloured red, the xylem generally yellow , 
the sieve-tubes blue , and the bast-fibres brown. 
Fig. 8. Part of a transverse section from a similar root, showing a secondary 
ray in which interxylary phloem has been formed, x 150. 
Figs. 9-12. Chironia peduncularis. 
Fig. 9. Part of a transverse section of an octarch root, moderately thickened, 
to show general structure, ph 2 is here the approximately central group of medul- 
lary phloem. Two protoxylem-elements are seen to the outside of the cambium. 
An intermediate one has become imbedded in the secondary wood, x 150. 
