Tuber.

Tuber. This is one of the forms of subterranean stems, and is formed by a part of the stem becoming thick and fleshy. This tissue is of a simple parenchymatous nature (see TISSUE), well filled with starchy matter, which serves as a store of food material for the plant, and especially as a stock in trade for the young plants which often grow from the buds of the tuber to begin life upon. These buds, together with the minute scales in the axils of which they occur, show that tubers are not, as they are commonly thought to be, Roots (q.v.). The true roots arise from the tubers. The potato (Solanum tuberosum) is the most familiar example. The buds in this case are called 'eyes.' If they are cut off the tuber and set in the ground they grow into new plants. This is the method adopted by gardeners for the propagation of the potato plant. It has been observed that the ordinary aerial buds show a tendency, occasionally, to become tuberous. This is taken advantage of by gardeners, who, by surrounding the lower part of the stem with earth, cause the buried buds, which would normally grow into branches, to become tubers. The Jerusalem artichoke (Helianthus tuberosus) is another common tuber. The subterranean fructification of a group of fungi, the Tuberaceæ or Truffles (q.v.) are called tubers.