the Sweet Potato. 209 
of the tubular piece, both passing down into the soil and 
becoming functional. 
HistoLocy oF NORMAL AND OF RING-FASCIATED SHOOTS.— 
For a better understanding of the cross-section of the ring- 
fasciated stem, we may first review the structure of the normal 
stem (Fig. 2). There is a cutinized epidermis bearing stomata, 
nectar glands’ and pedicellate hairs; internal to it is the 
green cortex, bounded on its inner face by a distinct starch- 
bearing bundle-sheath. Within this is a ring of bast fibres, 
then true phloem, cambium, xylem with many confused and 
insignificant medullary rays, and an unbroken pith. Numerous 
patches of internal phlcem that constitute a bicollateral bundle 
system lie between the xylem and the pith, as is frequently 
the case in Convolvulacee and allied orders. Milk canals 
are numerous in pith and cortex. 
The ring-fasciated stem shows a doubling of the above 
structure, in that the internal cavity is surrounded by epidermis, 
cortex, and a fibro-vascular ring in addition to those forming 
the normal external wall of the stem. We find, therefore, in 
cross-section of the anomalous stem, the following zones, 
passing from without inward (Fig. 4): epidermis (4%.) with 
cuticle, nectar-glands and pedicellate hairs, cortex (Co.), 
bundle-sheath (B. S.), bast fibre ring (B. F.), normal phloem 
(Ph.), cambium (Ca.), xylem (Xy.), internal phloem (/. P/.), 
1 Poulsen (18) describes nectar glands situated in pits at the top of the petiole 
of ‘‘ Batatas edulis’? (= Zpomea Batatas Poir.), but makes no mention of simi- 
lar, though less specialized, glandular hairs which occur on the lamina and on the 
stem of the plant. They are identical in structure and development with those 
described and figured by Ewart (6) for bomea paniculata. They are so plenti- 
ful on the apex of the stem and on the young leaf rudiments as to cover fully 
seven-eighths of the surface of those parts. As the parts grow older ‘the glandu- 
lar hairs become brown and shrivelled, and most of them fall off. On mature leaves 
they were found beset with a fungus, as also were the petiolar nectaries ; the 
parasite was evidently feeding on the nectar. Poulsen says ants and aphides are 
likewise attracted to the sweet potato tips ; the former doubtless serve as a protec- 
tive bodyguard against caterpillars, grasshoppers, snails, and the like. 
14 
