THE POTATO 7 



situated in a slight depression. These buds are known as the 

 " eyes " of the potato. The tuber, which may be whitish, brown, 

 or red on the surface, has a covering layer of cork, which prevents 

 any serious loss of water when the tuber is exposed on the surface 

 of the ground. The substance of the tuber is white, all the cells 

 being packed full of grains of starch. The presence of this gives 

 value to the tuber as an article of human food. It supplies, 

 however, only the starchy constituent of the food, the pro- 

 portion of stored nitrogenous substance being almost negligible. 

 The existence of the tubers is not explained by the accident that 

 they have been found of use to man. They are developed for the 

 use of the plant as a special means of its vegetative reproduction. 

 In reproducing the plant in cultivation the tubers are thus put 

 to the use for which they were evolved in nature. 



To grow a Potato plant, the gardener takes a medium sized 

 tuber and plants it some inches below the surface of the soil. 

 It is not absolutely necessary to take an entire tuber. It is 

 sufficient that the portion should have at least one bud or " eye" 

 upon it. The bud starts to grow into a shoot at the expense 

 of the starch stored within the tuber. When the shoot has ex- 

 panded above the soil, and roots have developed from the lower 

 portions of the stem, the plant is independent of this store, which 

 by this time is exhausted. The old tuber then decays. In nature, 

 when plants died down after flowering and fruiting, tubers, borne 

 on underground branches, would remain in the soil and give rise 

 to plants in the next season. The tubers thus serve to carry on 

 the growth of the plant from year to year, and also, since a 

 number are formed, to multiply the plant. The new plants will 

 spring up on the spot occupied by the parent, but if the soil is 

 disturbed, as might occur by animals rooting up the tubers for 

 food, they may be displaced to some distance and spread the 

 plant. Here and there in a garden a plant may be seen springing 

 up from a tuber left unnoticed in the soil from last year. Such 

 stray Potato plants illustrate the way in which the plant would 

 be naturally reproduced. 



If a plant developed from a tuber when fully grown is care- 

 fully dug up and examined it will be found to show the parts 

 represented in the accompanying plate. The one or more main 



