234 
Journal of Agricultural Research 
Vol. XIV, No. 6 
several axillary buds and undeveloped internodes. The central bud of 
an eye is most prominent and develops first upon renewal of growth. 
The spiral of the eyes of the tuber is usually left, though De Vries (7) 
records right spirals also, the latter type less frequent. 
Sections through the mature tuber show several zones of tissue readily 
distinguishable to the naked eye. These zones are the cortex with its 
periderm, the vascular ring, and the pith. Of these three areas the 
vascular tissue is least, the pith most prominent. In the region of the 
eye the vascular tissue approaches the surface of the tuber and provides 
vascular connection between the developing buds and the reserve mate¬ 
rials stored in the tuber. 
The amount of the vascular tissue of the tuber is only slightly greater 
than that of the stolon; but the individual groups are much separated 
in the expanded tuber, being only here and there united by interfascicular 
cambium. The xylem is mostly primary in nature, and only in the region 
of the larger groups are porous vessels of secondary xylem found. As 
will be shown in the developmental study of the tuber, the phloem 
becomes more and more broken up into small strands which are found 
scattered throughout the cortex and pith. The cortex and the pith 
differ mainly in the relative amount of cellular density, the cortex being 
more dense on account of the smaller size of its cells and the larger 
amount of cell content other than starch. 
A periderm 6 to 10 cells in thickness covers the entire tuber. The 
homogeneity of this layer is broken by small lenticel-like structures 
which are concerned with the aeration and which have developed below 
the position of the stomata of the young stolon tip. 
THE FLOWER 
The flowers are borne on short bractless pedicels which show the his¬ 
tological features characteristic of the stem (PI. 40, A). The vascular 
tissue, however, forms a more or less continuous band instead of being 
arranged in distinct groups (fig. 2, A, a). With the broadening of the 
pedicel to form the torus of the flower the band of vascular tissue becomes 
broken through the separation of five vascular strands (fig. 2, B, b), 
which diverge to occupy a position in the outer cortex—that is, the 
peripheral region of the cortex (fig. 2, C, b). 
When these groups have become distinct—in fact, even a little earlier— 
almost all of the remaining vascular tissue, c, of the cylinder now more 
or less reunited (fig. 2, D, c), passes out obliquely to form 10 separate 
bundles, d, in the inner cortex (fig. 2, E, d). The tissue which does not 
pass out is in two elongated groups which soon divide (fig. 2, E, e), each 
giving rise to two small groups of unequal size which, when entirely 
free, occupy the four quadrants of a circle (fig. 2, E, e; F, e). 
Of the 10 inner cortical groups, d, the five which alternate with b 
begin to expand and divide (fig. 2, F, f). Each one cuts off by radial 
