Mar. 15, 1924 
Studies on the Potato Tuber 
821 
In structure and tissue differentiation the resting bud resembles a 
stolon tip. The apical region, well protected by overlapping scales, is 
composed of a mass of cells rich in protoplasm. The walls are thin and 
of cellulose except for the outer wall of the epidermis, which is covered 
by a thin cuticle. Since the latter is devoid of a cellulose basis, as shown 
for other plants by Priestley, parasitic fungi which secrete cytolytic 
enzymes can penetrate the cuticle only by force of hydrostatic pressure. 
Where the bud merges into the tuber, differentiation into the charac¬ 
teristic tissue region takes place and the vascular tissue of the bud and 
bud scales joins the vascular ring of the tuber, which in the region of 
the eyes closely approaches the periphery. Like the vascular ring, the 
pith retains its connection with the lateral members of the tuber in that 
branches of the pith continue directly into the eyes. Since all the eyes 
thus maintain a connection with the central pith, sections through any 
part of the tuber show a system of such connecting strands of pith 
radiating from the center toward the periphery. The size and shape of 
these pith connections are similar in tubers of a given variety, and may, 
as will be shown later, serve as a group character. 
With the termination of the growing season, the tuber has completed 
its development; the bulk of the tissue has matured and becomes filled 
with reserve materials, chiefly in the form of starch. Only small, res¬ 
tricted areas of the tuber, the buds, possess meristematic tissue, ready 
to resume life activity with the completion of the rest period and when 
external conditions permit of cell division and growth. Since the tuber 
is a shoot with indeterminate growth, the central bud is the youngest 
and should normally resume growth first. However, the prolonged 
state of dormancy which affects all eyes equally should have a leveling 
influence and remove whatever advantage the terminal eye may have 
possessed. Yet the earlier development of the apical buds is a fact, and 
to explain it various theories have been considered. 
Franz (6), in his anatomical studies of the potato tuber, noticed that 
the terminal eye was shallow and not buried in cortical tissue; that the 
cells in the vicinity of the bud contained more water and were richer 
than elsewhere in protein; that the pith formed a direct and broad con¬ 
nection with the apical bud; and since the latter was also ontogenetically 
the youngest he concluded that the morphological and chemical differ¬ 
ences sufficed to account for the earlier development of the terminal eye. 
While the evidence brought forward by Franz may not be contested, 
it must be remembered, nevertheless, that the vascular tissue of the 
tuber, no matter whether it connects to lateral or terminal buds, is at 
best only weakly developed and that the repressive effect of a thick cor¬ 
tical tissue appears nowhere in evidence. The direct and more massive 
pith connection and the broader point of contact which the terminal eye 
forms with the vascular tissue are undoubtedly advantages which the 
lateral eyes lack. This fact is emphasized by the results of some experi¬ 
ments 'of Miss Femald, 3 who found a rather definite correlation between 
the osmotic concentration of the tissues around the eyes and the tendency 
for these eyes to sprout. While Miss Femald’s results may explain why 
the basal eyes are inhibited, they in no way explain why the apical eyes 
get the earlier start. The morphological advantages which the apical 
eye possesses over the basal ones, as shown above, seem to offer the 
most reasonable explanation for the observed dominance. 
•Fernald, Evelyn I. the inhibition or bud development as correlated with osmotic concen¬ 
tration. (Title.) In Amer. Assoc. Adv. Sci. Program 76th Meeting, p. 94, 1922. 
