. Botany, with agricultural applications. Botany. 280 LEAVES Beans, etc. About 15 percent of the dry weight of Irish Potatoes is starch, and in roots, stems, leaves, and in fruits it is present in considerable amounts. Its abundance and wide distribution is due to the fact that it is the chief form in which plants store food. In leaves, when photosynthesis is active and sugar is being formed more rapidly than carried away, the surplus sugar is changed to starch and thus temporarily stored until the starch is changed back to sugar to be transported to other parts of the plant. In seeds starch i
. Botany, with agricultural applications. Botany. 280 LEAVES Beans, etc. About 15 percent of the dry weight of Irish Potatoes is starch, and in roots, stems, leaves, and in fruits it is present in considerable amounts. Its abundance and wide distribution is due to the fact that it is the chief form in which plants store food. In leaves, when photosynthesis is active and sugar is being formed more rapidly than carried away, the surplus sugar is changed to starch and thus temporarily stored until the starch is changed back to sugar to be transported to other parts of the plant. In seeds starch is stored to serve as food for the young plant during germination. In tubers, roots, and stems starch is stored to be used in new growth. Unhke the sugars starch is insoluble in the cell sap. It occurs as definitely shaped bodies, known as starch grains with size, shape and markings different, in most cases, in different species of plants {Fig. 250). So characteristic are the size shape, and mark- ings of the starch grains of many plants that they are used in identifying adulter- ants in ground vegetable products. Sugar is transformed to starch by the chloroplasts and plastids, and starch grains may be so numerous within cells as to almost entirely ^-^.y - I \ ' fill the cell cavities. ° c Starch and cellulose have the same form- ^ „^„ , , ula (C6Hio06)n, but the n in the starch Fig. 250. —a, starch i • j j. i, j-£c 4. grains of Irish Potato; formula is supposed to have a different fc, starch grains of Wheat; value, and possibly there is a different ar- c, starch grains of Corn, rangement of atoms, for the two substances have very different properties. Starch is readUy decomposed by enzymes and artificially by acids into dextrin, maltose, and glucose, the product depending upon the extent to which the starch molecule is decomposed. Starch and the sugars constitute the basic foods for animals. The value of cereals and most all seeds for food is chiefly due to the starch
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Keywords: ., bookcentury1900, bookdecade1920, booksubjectbotany, bookyear1920
