JOURNAL OF AfflCOLim RESEARCH 
Vol. XXVII Washington, D. C., March 15, 1924 No. 11 
STUDIES ON THE POTATO TUBER 1 
By Ernst Artschwager 
Assistant Pathologist , Office of Cotton , Truck , and Forage Crop Disease Investigations , 
Bureau of Plant Industry , United States Department of Agriculture 
INTRODUCTION 
# 
A potato tuber is morphologically a modified stem with its axis greatly 
shortened and its lateral members only weakly developed, the latter 
forming what are known as the “potato eyes.” 
The tuber originates as a stolon from an axillary bud of the underground 
stem. At first clavate, the young organ soon assumes the shape char¬ 
acteristic of the variety. After a brief period of radial expansion, rapid 
apical growth becomes evident, new leaf scales are progressively differenti¬ 
ated from the vegetative cone, and in the axils of these scales new eyes 
and buds develop to maturity. Simultaneously with apical growth 
intercalary stretching occurs, whereby the spaces between the nodes 
widen and the spiral arrangement of the eyes becomes more distinct. 
The close relationship between tuber and stem, already evident from 
the grosser morphological features, becomes incontestable when the 
anatomical, structure and the ontogeny of the tissues are studied. In 
their early development both tuber and stem show practically the same 
organization; both have a bicollateral stele limited externally by a well 
developed cortex, internally by the pith. In their further development, 
however, each organ differentiates in accordance with the r 61 e which 
it is destined to play in the life of the plant. The stem, primarily an 
organ for support, develops a large amount of mechanical tissue and 
cells for water conduction—its vascular cylinder becomes hard and 
woody. The tuber, on the other hand, developing under the protective 
covering of the soil and destined to become an organ for storage, gives 
rise, as will be shown later, to a large amount of unspecialized parenchyma 
tissue. The different r 61 e of these two organs as indicated by their 
structural make-up is destined conversely to affect their outward ap¬ 
pearance; that is, the stem will grow to a considerable length and remain 
slender, while the tuber will expand laterally as the flow of organic 
food material, constantly moving downward from the leaves, furnishes 
the Bausteine for new cells and tissues and for reserve starch which fills 
the cells as soon as they differentiate and mature. 
STRUCTURE OF THE STOLON PRIOR TO TUBER FORMATION 
A median section through a stolon tip shows close behind the growing 
region three distinct tissue zones—the dermatogen, the procambium, and 
the fundamental meristem. These tissues become greatly extended and 
differentiated as the stolon tip develops into a tuber. 
The dermatogen of the growing point becomes a single-layered epi¬ 
dermis.* In surface view its young cells are square or hexagonal and 
more or less isodiametric. In maturing the cells become stretched in the 
1 Accepted for publication Nov. 24,1923. 
Journal of Agricultural Research, 
Washington, D. C. 
(809) 
Vol. XXVII, No. « 
Mar. 15, 1924 
Key No. G-36J 
85606—24 - 1 
