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Ethel N. Thomas. 
Fig. 27. Triangular solenostele of stem at beginning of departure of leaf- 
trace. Two accessory steles in ground tissue, and one across future leaf- 
gap- 
Fig. 28. Leaf trace becoming divided into bundles of Series a. 
Fig. 29. Ditto, further advanced. Root passing out on left. 
Figs. 30, 31. Further differentiation of bundles of Series a, and involution 
of the sides of trace to form Series b. 
Fig. 32. Fusion of penultimate portions of trace to form large bundle from 
which Series c will arise. 
Fig. 33. Commencement of differentiation of bundles of Series c from ends 
of trace. 
is effected by sclerenchymatous elements, which, penetrating the 
vascular tissue from both sides, isolate portions of it, and thus give 
rise to the bundles of Series a (Text-figs. 28 and 29). 
The sides of the original horseshoe now become infolded, and 
at the same time give off bundles forming the inverted Series b 
(Text figs. 30, 31, and 32). 
Fig. 34. 
Fig. 34. Base of young petiole. Series a consists of six bundles; Scries b of 
four. The large bundle is the only representative of Series c, while the 
bundles on each side of it belong to Series d. N.B. Px. groups indicated 
by black dots as also in Figs 35 and 36. 
Fig. 35. 
Fig. 35. Older petiole, some distance from base. Series a composed of 
many bundles and forming a continuous curve with the inverted bundles 
of Series b. Series c composed of three bundles. Series d forms a row 
along the flattened upper surface. (Sec E of Fig. 37.) 
The portions of the horseshoe just below the involuted sides 
