6), the tubers being partly radical partly budlike in their character.
Salep, still used in the Levant, consists of the dried tubers of a terrestrial orchid, and contains a relatively large amount of nutritious matter.
The tubers of Ipomaea Batatas are rich in starch and sugar, and, as the "sweet potato," form one of the most widely distributed foods in the warmer parts of the earth.
All plant life has a remarkably large proportion of subterranean growth, because of the necessity of getting moisture from the earth and not from the air; hence roots and tubers are unusually well developed.
A highly specialized means of vegetative reproduction is seen in the tubers of Phylloglossum and the embryos of some Lycopods.