The potato tuber consists mainly of a mass of cells filled with starch and encircled by a thin corky rind.
The leaf scar is protected by a corky change (suberization) in the walls of the exposed cells.
Both cuticularized and suberized membranes are insoluble in cuprammonia, and are colored yellow or brown in a soltition of chlor-iodide of zinc. It is probable that the corky or suberized cells do not contain any cellulose (Gilson, Wisselingh); whilst cuticularized cells are only modified in their outer layers, cellulose inner layers being still recognizable.
The corky layers which take so prominent a share in the formation of the bark are similarly modified and subserve the same purpose.
We thought the tissued, infiltrated head of the Sperm Whale, was the lightest and most corky part about him; and yet thou makest it sink in an element of a far greater specific gravity than itself.
Bast mats are now made chiefly in Russia, the bark being cut in long strips, when the liber is easily separable from the corky superficial layer.