POTATOES AND OTHER STARCHY ROOTS AS FOOD. S 
up to the light four distinct parts may be seen (fig. 1). The outer 
skin consists of a thin, grayish-brown, corky substance correspond- 
ing roughly to the bark of an above-ground stem, which is of 
Fig. 1. — Transverse and longitudinal sections of the potato : a, Skin ; h, cor- 
tical layer ; c, outer medullary layer ; d, inner medullary area. 
Fig. 2. — Changes of starch cells in cooking : a, Cells of a raw potato with starch grains 
in natural condition ; b, cells of a partially cooked potato ; c, cells of a thoroughly 
boiled potato. 
little value as food (see p. 5). The cortical layer (bark) is next 
to the skin and may be from 0.12 to 0.5 inch in thickness. This 
layer is slightly colored and turns green if exposed to the light for 
some time, thus showing its relation to the tender green layer beneath 
