The potato tuber consists mainly of a mass of cells filled with starch and encircled by a thin corky rind.
The plants generally have a rhizome bearing radical leaves, as in asphodel, rarely a stem with a tuft of leaves as in Aloe, very rarely a tuber (Eriospermum) or bulb (Bowiea).
An orchis found in the mountain yields the dried tuber which affords the nutritious mucilage called salep; a good deal of this goes to India.
The so-called fir-cone potatoes, which are elongated and provided with scales at more or less regular intervals, show also very clearly that the tuber is only a thickened branch with "eyes" set in regular order, as in an ordinary shoot.
A second edition of the Herbal was published in 1636 by Thomas Johnson, with a different illustration from that given in the first edition, and one which in some respects, as in showing the true nature of the tuber, is superior to the first.