Leaves and flower stalks grow from the top and the roots emanate from the underside. Irises are probably the most instantly recognised of plants in this category. Root tubers are formed by roots that have transformed into storage organs and in the process have lost the ability to absorb nutrients in the usual manner. Other roots, normal in appearance, carry out this process for the plant. The buds are generally found on the collar at the base of the plant's main stem.
Dahlias have root tubers.
Only then will the aerial parts appear. These ensure food supplies, including those for the following year which means it is important not to disturb the plant whilst it is growing. If conditions are unfavourable bulbs will continue to develop underground, using energy reserves to create new scales or secondary bulbs. In this way some lilies will remain apparently dormant for a whole season. Although normal sexual reproduction occurs to produce seed, vegetative reproduction also occurs, producing plants identical to the parent.