THE POTATO IN BRITISH COLUMBIA. 



9 



fundamentally the same, and the underground form can be changed into a typical 

 leafy shoot if brought above ground. The rhizomes, or stolons, are not to be confused 

 with the real roots, which are slender fibres ramifying through the soil to a depth of 

 2 to 4 feet. The stolons are short, 1 to 4 inches long, and the tuber is formed by the 

 thickening of the free end (Fig. 2). The "tubers," then, are simply terminal 

 portions of the underground stems swollen with reserve food in the form of starch. 



At the " stem-end " the remains of the stolon can usually be found, while at 

 intervals over the surface the " eyes " occur, each eye being a bud, or more correctly 

 a cluster of buds. The tuber consists of the following parts (Fig. 3) : 



(1.) Periderm, or skin, which comprises the corky covering of the tuber. On 

 Hi.- skin, ns on the woody bark of trees and other plants, ;ire "lenticels" (Fig. 4), 

 or pores, closely filled with cells and serving as a channel for the admission of air 

 to the internal tissues. Ordinarily they are hardly noticeable, but in the case of 

 tubers grown on wet soil they increase in size, and when the tubers are freshly 

 iluu' ure white and glistening. Such tubers are often mistakenly considered to be 

 diseased. 



Fig. 3. Cross-section of a potato (original). 



(2.) Cortex, or layer just inside the skin. This is very rich in starch. 



(3.) Vascular ring. This contains the vascular bundles, which include the sap- 

 vessel. It is this ring that turns brown at the stem-end of the tuber when the 

 wilt-fungus is present. 



(4.) Medulla, or pith. This Includes everything inside the vascular ring and 

 comprises the greater portion of the tuber. It consists of an outer dense layer and 

 an inner lighter, more or less star-shaped area, poorer in starch. 



The " eyes " are arranged in a spiral around the tuber, close together at the 

 end remote from the " stem-end." This is termed the " seed-end," " eye-end," or 

 "rose-end." Each eye is formed in the axil of a small scale-leaf, which disappears 

 as the tuber matures. The strongest eyes are found at the " seed-end." The number 



