.Mar. 15,1924 
Studies on the Potato Tuber 
819 
independent origin and in no way related to the vascular cylinder. 
However, the ontogeny of the vascular tissue, especially of the isolated 
groups of phloem and their subsequent development, excludes such a 
theory. 
THE POTATO EYE 
The potato eye is a leaf scar with its subtended axil, which contains 
a suppressed lateral bud and undeveloped intemodes. The eyes in their 
entirety show a definite arrangement in the form of a spiral (fig. 4), the 
direction of propagation of which is, according to the variety and the 
individual, either right or left. The arrangement of the eyes is thirteen 
ranked, since the fourteenth eye is over the first after five turns of the 
spiral. Each eye contains at least three buds arranged in the form of 
an obtuse triangle and protected by more or less conspicuous scales 
(fig. 5). Often, however, a larger number of buds are present which 
then form a secondary spiral to the left if the main spiral of the eyes is 
dextrorse, or conversely if the latter is sinistrorse. 
The eyes of the tuber vary greatly in size and form, and the difference 
is further emphasized through the influence of environmental factors 
which affect the development of the plant in general. There are shallow 
and deep-eyed varieties, and between the two extremes all intermediate 
types may be found. In a given tuber the lowest basal eye is small and 
inconspicuous; the eyes in immediate succession are larger and may 
protrude. After the first or second turn of the spiral the eyes become 
uniform and characteristic of the variety. The apical eye cluster is 
commonly not in direct line with the main axis, but excentric; the eyes 
composing it are small and contain fewer buds than those of the body of 
the tuber. There is, furthermore, a variation in the depth of these eyes. 
Some are very protuberant, but most are quite shallow. 
A median longitudinal section of a stolon tip prior to tuberization shows 
the apical growing point with its protective scales and a number of buds 
developing in the axils of scaly leaves (PI. 3). As the tuber enlarges, 
new buds are constantly differentiated from the growing apex, while 
the older ones gradually develop to maturity. In this growth and differ¬ 
entiation the scales, once very prominent, show a decided lag in develop¬ 
ment, and finally atrophy, leaving a mere scar, the “brow” of the mature 
eye. The size and form of the brow is correlated with the depth of the 
eyes. As a rule, the deeper the eye the more prominent the brow. 
