162 
Journal of Agricultural Research 
Vol. XXVII, No. 3 
pass through the cortex, and continue vertically through the veins. The 
gap produced in the primary vascular ring is filled by a new partial cam¬ 
bium and its products. Small bundles are occasionally seen in the pe¬ 
ripheral cortex even when the projecting ridges are wanting. In the case 
of large veins, a narrow band of tissue, a special layer visible even to the 
naked eye and not unlike an abscission layer, separates the vein tissue 
and its bundles from the cortex of the large fleshy root. 
The endodermis and primary cortex continue to show a lag in develop¬ 
ment. Tangential stretching of the cells of the endodermis is still evi¬ 
dent, even while anticlinal walls appear at intervals. A periderm is 
gradually laid down in the superficial cell layers, the epidermis and the 
peripheral cells of the cortex, and while this layer is increasing in thick¬ 
ness the original cortex and the 
endodermis become practically ex¬ 
tinct. 
Thus continued growth and dif¬ 
ferentiation give rise to a perplex¬ 
ing anomalous structure which 
becomes intelligible only when the 
earliest developmental processes in 
the young organ are followed out. 
THE MATURE FEESHY ROOT 
The fully grown fleshy root 
shows in transverse section a nar¬ 
row cortex protected by a periderm, 
and a central core of storage 
parenchyma in which numerous 
strands of vascular tissue are em¬ 
bedded. The continuity ‘ of the 
cambium ring which separates these 
Fig. 4 .—Diagrammatic drawing of cross section of tWO tlSSUeS is broken in places, tO 
mature fleshy root showing the projecting ridges allow for the nassitlp- Ollt of root 
with their vascular tissue. diiuw uic pacing uui ui iuul 
traces which traverse the fleshy 
root radially and connect with the lateral rootlets; and for the continua¬ 
tion of cortical traces upward in the projecting veins, where such are 
present. In certain varieties a second apparent break is produced by nar¬ 
row invaginations of the cambium (PI. 3, A, B), which commonly have only 
a slight vertical depth, sometimes not exceeding the diameter of a root 
trace. The formation of these invaginations can be related to the early 
growth of the root, and constitutes a localized delayed development of 
the cambium. 
The tissue internal to the cambium consists of two types: (1) a periph¬ 
eral zone in which the xylem elements show a typical radial arrangement 
and which is largely the product of the primary cambium; (2) a core 
of vascular tissue embedded in storage parenchyma. The individual 
strands of the vascular tissue are surrounded by a circular or partial 
cambium. The larger vascular strands of the central core occur in one 
or another of three general types: (a) the groups are distinct and arranged 
at the periphery of a narrow circle (PI. 3, A); (b) the groups are scattered 
much like the vascular bundles in a com stalk (fig. 4); (c) the bundles 
open up, join each other laterally and form in their entirety an intricate 
network which makes it impossible to trace the individual component 
