Early tuber development from explanted stolon nodes of Solanum tuberosum var. Kennebec [Potato]

Tubers are initiated within 4 days when cultured stolon pieces with axillary buds are grown on medium with high (12%) sucrose levels. A comparison of several stages of tuber ontogeny with the initial explant showed that enlargement of cortical and pith cells accounts for the initial radial expansion of tubers. Later, phellogen activity and limited vascular cambium activity also increase tuber diameter. Although divisions occur in both the hypodermis and epidermis early in tuber growth, the phellogen layer arises from the hypodermis. Lenticels form below each stomate. Vascular parenchyma cells, unlike cortical and pith cells, store very little starch. Plastids of these cells possess few internal thylakoids but a considerable amount of lipid-like material.