Tuber eyes and sprouts
The number of eyes in a tuber varies considerably depending on many factors such as variety, size of tuber and growth conditions.
Twelve to 15 eyes are quite usual in a 45 mm 'Bintje' tuber.
They form a special spiral round the tuber, like the side buds on a stem. The sheath surrounding the buds in the eye is a rudiment of a leaf. The eye is, in fact, the axil of a leaf on part of a stem.
In many cases the main bud lies in the middle of the eye, with a bud on either side, often clearly separated by tuber flesh. These side buds may be regarded as the lowest lateral buds of a sprout, which have become separated by the growth of the tuber.
Normal sprouts can, and often do, grow from them. The main sprout also bears lateral buds which can form lateral stems or stolons. If the sprout breaks off but its base remains, there is a fair chance that the bottom lateral buds, which would normally form stolons, will grow into one or more stems, all of which arise from the same eye. In the case of a sprout which has been allowed to develop in light to an advanced stage, the lateral buds will have sprouted far enough for the terminal and lateral buds to be visible on them also .