578 BOTANY OF CROP PLANTS 



the only one to develop. The sprout produced by the ter- 

 minal eye is spoken of as the "master sprout." The eyes 

 vary in different varieties from very deep to level with the 

 surface; the latter condition results in smooth potatoes. 

 Deep eyes tend to hold moisture ; as a result, decay is invited 

 and hastened when the potatoes are stored. Smooth varie- 

 ties occasionally give rise to deep-eyed tubers, although, as 

 a rule, eye depth is maintained by tuber propagation. It is 

 likely that the deeper-eyed plants give rise also to smooth 

 tubers and that in seed propagation the same results follow 

 as in the case of form and color. 



The number of eyes varies considerably within the same 

 variety; in one case. Rural N^w Yorker, it ranges from 7 to 

 28; and in Early Ohio, from 7 to 22. The number of eyes 

 affects the quality, since the poorer zone of the potato (in- 

 ternal medulla) extends a branch to each eye, thereby in- 

 creasing the percentage of internal medulla at the expense 

 of the two outermost valuable layers. 



Germination or Sprouting of Tuber. — Potatoes undergo 

 some changes in storage. Not only do they lose water and 

 decrease in weight but they increase in sugar. When sprout- 

 ing commences, the potato becomes sweeter, due to the con- 

 version of starch into sugar by the enzyme diastase. The 

 most vigorous buds are the terminal ones. The tip of the 

 main sprout grows upward. The underground stems bear 

 tubers at their ends. These will not tuber if brought to the 

 light but will develop into ordinary green-leafed shoots. 



Physical Composition of Potatoes. — In all varieties the 

 cells of the cortex are much smaller than those of the medulla. 

 In general, potato varieties are characterized by their 

 cellular density and can be grouped accordingly. The 

 groups are not, however, clear-cut. Cellular density is an 

 important factor to consider in the breeding of potatoes for 



