Aug. s, 1918 
Anatomy of the Potato Plant 
233 
Except for stomatal openings, the epidermis completely covers the leaf 
and is closely similar to that of the young stem. Stomata are found on 
both the lower and upper side, but are far more numerous on the lower 
surface. The stomata as seen in Plate 36, E, are of a simple type. The 
pores are surrounded by a pair of specialized guard cells which contain 
numerous chloroplasts; accessory cells are not present. The air cham¬ 
bers are small and are formed by the reduction in the size and by the 
arrangement of the subepidermal cells. 
N THE ROOT 
A cross section through a small fibrous root (PI. 37, B) shows a central 
core of vascular tissue, limited on the outside by an endodermis and 
cortex. The latter varies in extent with the size and age of the organ, 
being most prominent in young, small roots, and becoming less con¬ 
spicuous in old, mature structures. The peripheral cells of the young 
cortex are covered by a “root epidermis,” which, however, in old roots 
becomes tom and is sloughed off. The traces of vascular tissue supply¬ 
ing the lateral rootlets arise in the pericycle, and are given off directly 
and without branching or complication. Since the amount of primary 
structures is very insignificant, and most of the tissue of older roots is 
secondary in origin, the structure of the root will best be studied in its 
development, and for that reason will be discussed in detail in the section 
on ontogeny. 
THE STOEONS 
The stolons arise exogenously from the underground portion of the 
stem, which they resemble in structure and arrangement of tissues, 
except for a reduction in the amount of xylem, and absence of specialized 
mechanical tissue (PI. 38, A). There are few xylem elements and 
these are vessels; tracheids are even less plentiful. Collenchyma is 
entirely wanting, and the epidermis does not show the specialization 
found in the aerial portion of the plant. The vascular strands of the 
stele, which when young are separated by gaps, are later incompletely 
united by means of an interfascicular cambium, which gives rise to some 
secondary growth. Fibers are found both in the inner and in the outer 
phloem, but they appear very late in the ontogeny of the organ. Accord¬ 
ing to Reed (ji), the endodermis here contains no starch even when the 
surrounding cortical tissue is crowded with starch grains, and this study 
confirms his observation, inasmuch as there is far less starch in the endo¬ 
dermis than elsewhere. The reverse is true for the endodermis of the 
stem. The cells of cortex and pith show no feature of interest, being 
of the type observed in the stem. 
THE TUBER 
The potato tuber is morphologically a shortened, thickened stem with 
scalelike leaves, or leaf scars. The eye in its entirety is a leaf scar with 
its subtended axil, which contains a suppressed lateral branch with 
