A swollen underground stem or root in certain plants. It enables the plant to survive the winter or dry season and is also a means of propagation. A stem tuber, such as the potato, forms at the end of an underground stem. Each tuber represents several nodes and internodes. The following season several new plants develop from the terminal and axillary buds (eyes). Root tubers, such as those of the dahlia, are modified food-storing adventitious roots and may also give rise to new plants.