520 Introduction to the Study of Science 



252. The plant's use of foods. What is done with the sugars 

 and starch, the proteins, fats, and oils which plants manufac- 

 ture? Leaves, as you have demonstrated, do not, when left 

 in the dark, retain the food they create by means of the sun- 

 light. What disposition is made of the food? Part of it is 

 immediately consumed in the work of respiration and manu- 

 facture of food. Part of it is digested and distributed as nu- 

 trition to the mature plant cells which are actively at work in 

 different parts of the plant, and for the making of cellulose to 

 thicken cell walls. Wood is largely cellulose ; cotton is prac- 

 tically pure cellulose. Part of the food is utilized in producing 

 new cells and cell walls wherever growth is taking place, as in 

 buds, stems, and roots. A part is used in making various com- 

 pounds which give odor and color to flowers, and flavors to 

 fruit and seed. Or it may remain in the sap as sugar. What 

 plants do you know that have sweet sap? What use do we 

 make of such sap ? 



253. Where plants store food. As plants mature or ap- 

 proach the end of their annual growth they manufacture more 

 food than they can make use of in the ways just stated. The 

 excess food is transferred and deposited in reserve food centers 

 for future use. Such reserve centers are seeds, buds, stems, 

 roots and root stalks, tubers, and bulbs. Many plants, as corn, 

 wheat, oats, barley, beans, and peas, store this in grains or 

 seeds to serve as nutriment for their offspring in early growth. 

 Where do potatoes lay up this reserve? Where do such plants 

 as carrots, beets, sweet potatoes, parsnips, and turnips accumu- 

 late their food supply? For what purpose? Where do the 

 onion, lily, and similar plants deposit it? Trees not only pro- 

 vide their young in seeds with nutriment, but also lay up a 

 sufficient supply in special parts for beginning their own growth 

 the succeeding season. 



Exercise : Tests of food storage. As starch is the most common 

 of the foods deposited in solid form, it is worth while to make a series 

 of tests on different parts and products of plants to determine its 



