A tuber is a prominently thickened portion of a root or stem, and it is usually subterranean. The potato, sweet potato and dahlia furnish good examples. Tuberiferous plants are multiplied by planting these tubers whole, or the tubers may be cut into small portions as described in [Chapter IV], in the descriptions of cuttings. In hardy species, the tubers may be allowed to remain in the ground during winter, but they are generally dug in the fall and stored in a dry and cold place, but where they will not freeze.
An offset is a crown or rosette of leaves, usually borne next the surface of the ground, which detaches itself and forms an independent plant. The best examples occur in the house-leeks, plants which are more familiarly known as “hen and chickens” and “man and wife.” These offsets take root readily, and in propagating there is no other care necessary than to remove and plant them.
A crown is a detachable portion of a root-stock bearing roots and a prominent bud. Rhizomes or root-stocks multiply individuals and extend the distribution of the species by means of a progressive movement of the crowns. The root-stock grows during summer, and at the end of the season each branch develops a strong terminal bud which usually produces a flowering stem the following season. The root-stock gradually dies away at its old extremity, and in a few years a single individual gives rise to a considerable patch. This is well shown by the common May-Apple or podophyllum.
Fig. 17. Lily of the Valley Crown.
In some species these crowns are removed in the autumn and are planted and handled in much the same manner as bulbs. The crown or pip of the lily of the valley, shown half size in [Fig. 17], is obtained in this manner.