What Are Bulbs And Stem Tubers?


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A bulb is a modified shoot consisting of a flattened, disc-like stem with closely set nodes bearing fleshy scale leaves surrounded by some dry scale leaves. Buds arise in the axils of the fleshy scale leaves. In the bulb the food (mainly sugar) is stored in the fleshy scale leaves and not in the stem as in the other underground storage stems. Adventitious roots are found at the base of the stem.

Under favorable conditions the central, terminal bud grows into an aerial shoot using the food stored in the fleshy scale leaves. Once the leaves of the shoot are exposed to sunlight they are able to photosynthesize. The excess food is transported down to the axillary buds of the old underground stem. As more and more good material is stored in the axillary buds they grow to form new bulbs. Each bulb bears small buds as in the mother bulb.

A stem tuber is a swollen underground stem bearing a number of reduced scale leaves. Each leaf scar is recognizable as the "eyebrow" of the potato and the "eyes" of the tuber are actually buds. The food materials stored in the tuber are starch and proteins. The proteins are found mainly just beneath the skin.

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