ON THE ANATOMY OF THE SWEET POTATO ROOT, 
WITH NOTES ON INTERNAL BREAKDOWN 
By Ernst Artschwager 
Assistant Pathologist, Cotton, Truck, and Forage Crop Disease Investigations, Bureau of 
Plant Industry, United States Department of Agriculture 
INTRODUCTION 
The fleshy roots of the different varieties of Ipomoea batatas Lam. are 
fusiform, napiform, or irregular-spherical. The surface of the skin 
appears uniform and smooth in some varieties, and in others irregularly 
ribbed, because of the presence of vein-like prominences. The secondary 
roots are arranged in more or less straight vertical rows. Each of these 
rootlets sits in a shallow depression surrounded by an arch of rough, scar¬ 
like tissue, which in shape and texture closely resembles a potato eye. 
Occasionally the fleshy roots are deeply lobed so that the rows of lateral 
rootlets lie in longitudinal grooves. 
The root nature of these fleshy structures was first shown by Turpin 
(6) , 1 2 who published figures comparing the roots of Ipomoea to the tubers 
of the Irish potato and the Jerusalem artichoke. Recently Kamerling 
(3) and Tuyihusa (7) have taken exception to this view and claimed that 
these fleshy structures are modified stems. But the validity of this 
assumption, however ably defended otherwise, becomes untenable when 
young material is studied. The exarch position of the protoxylem 
decides, without further argument, in favor of the root-structure theory 
of these organs. 
Since the sweet potato belongs to a group of plants which are dis¬ 
tinguished by a peculiar anomalous growth, its anatomical structure 
has been studied indirectly by a number of investigators, notably by 
Schmitz (5). The only direct contribution to the knowledge of the 
internal structure of the sweet potato is a short treatise by Miss McCor¬ 
mick (4), who also has reviewed all pertinent literature. 
THE STRUCTURE OF THE YOUNG ROOT 
The young root shows in transverse section several groups of vascular 
tissue, separated from a thick cortex by an endodermis. (Fig. 1.) The 
vascular tissue is arranged radially, the xylem and phloem in alternating 
strands. The number of protoxylem points varies, but most of the roots 
are pentarch or hexarch. In the region near the growing point, the first 
protoxylem elements to mature are those farthest away from the center; 
the development therefore is centripetal. The later maturing protoxylem 
elements approach each other more and more closely with the increasing 
age of the region. The protophloem forms small, oval groups lying 
between the strands of protoxylem and within the circle of the youngest 
protoxylem element. A parenchymatous sheath, composed of small 
cells which lack intercellular spaces, intervenes between phloem and 
1 Accepted for publication Nov. 24, 1923. 
2 Reference is made by number (italic) to “ Literature cited,” p.. 166. 
(IS 7 ) 
Journal of Agricultural Research, 
Washington, B. C. 
Vol. XXVII, No. 3 
Jan. 19, 1024 
Key No. G-357 
