POTATOES AND OTHER STARCHY ROOTS AS FOOD. 13 



this important vegetable. If the tubers were originally affected with 

 rots these will go on developing until the potatoes are quite unfit for 

 food. If the skin, which is the natural protection of the tuber against 

 the minute forms of life which cause decay, has been broken or 

 bruised, the injured portion offers an entrance to bacteria, etc., which 

 will develop in them, especially if the potatoes are stored in a warm, 

 moist place. Aside from these abnormal changes there are others 

 which occur under the best of conditions. The potato, it must be 

 remembered, is not a dead thing, but one from which active plant life 

 will be renewed as soon as conditions are favorable. Even during 

 the latent winter period the protoplasm of the cells is constantly pro- 

 ducing minute changes known as " after ripening," in which part of 

 the sugar is broken down and carbonic acid and water are given off. 

 Part of the insoluble starch is also changed into dextrin and other 

 soluble forms. This is believed to be due to the action of ferments 

 normally present, which aid the plant by thus changing its stored 

 food into a form which can be used for new growth. The extent of 

 these changes seems to depend ordinarily on the age of the tuber and 

 the temperature at which it is kept. Everyone knows that potatoes 

 stored where it is warm sprout more readily than those kept in a cold 

 cellar. The older the tuber is, the more ready it will be to begin its 

 new growth and the more abundantly will the starch be converted into 

 sugars. This explains why old potatoes are less starchy and mealy 

 and sometimes sweeter than fresh ones. The temperature especially 

 affects the rapidity of new growth. This is one reason why potatoes 

 stored in a warm place are more likely to shrink than those in a 

 cool place. These facts also suggest why frozen potatoes have a 

 sweet taste; the change of starch into sugar by the enzyms goes on 

 regardless of the cold, but the activity of the cell protoplasm is 

 checked by the cold and the sugar accumulates instead of being broken 

 down. The sweet taste is more noticeable in tubers which have been 

 slowly frozen than in those subjected to a sudden cold, because the 

 sugar has had a longer opportunity to form. If frozen potatoes are 

 left for a few days in a moderate temperature part of the sugar will 

 revert to starch, and the sweet taste will in a measure disappear. Of 

 course, the amount of material which is changed during storage will 

 vary with the conditions, but sound potatoes properly stored should 

 not shrink more than 10 or 12 per cent. The most favorable tem- 

 perature for keeping potatoes is from 32° to 50° F., and if the store- 

 room is dry, well aired, and partly lighted, they are less likely to be 

 attacked by disease or harmful bacteria. 



Solanin, an acrid poisonous substance, which is characteristic of the 

 nightshade family, develops in unusual quantities in sprouting po- 

 tatoes and in those which have turned green from exposure to the 

 light. A trace of it (0.01 per cent) is present in ordinary potatoes 



