. Elementary biology; an introduction to the science of life. Biology. STARCH-MAKING AND DIGESTION 79 different kinds are known. They are peculiar in that they seem to induce chemical changes in other substances, zvithoiit, hozvever, undergoing any changes thcmsel'ves. As a result of this peculiarity a comparatively large amount of material may be made to undergo chemical change through the activity of a very small amount of enzym. 113. Food transportation. The cells of the chlorophyl-bearing tissues con- tain diastase and other ferments. In the light, some of the sugar that is formed passes o
. Elementary biology; an introduction to the science of life. Biology. STARCH-MAKING AND DIGESTION 79 different kinds are known. They are peculiar in that they seem to induce chemical changes in other substances, zvithoiit, hozvever, undergoing any changes thcmsel'ves. As a result of this peculiarity a comparatively large amount of material may be made to undergo chemical change through the activity of a very small amount of enzym. 113. Food transportation. The cells of the chlorophyl-bearing tissues con- tain diastase and other ferments. In the light, some of the sugar that is formed passes out of the pulp cells and is carried down in the bast, or phloem tubes (see p. 176). But under favorable conditions for food-making the sugar is manufactured faster than it can be car- ried away. Most of it is then converted into starch, which is insoluble. In this way it accumulates in the cells during the day. When darkness sets in, a dia- static action converts the starch into sugar, and this is then carried down into the stem or roots (see diagram, Fig. 26). This explains why leaves that are full of starch in the late afternoon show no signs of starch very early in the morning. As the morning light increases in intensity, starch is accumulated, and in the afternoon the cells are again full. From this we can also understand the presence of starch in potato tubers and in other organs that do not contain chlorophyl. The starch is formed in the cells of the tuber by the action of a ferment upon sugar. The sugar is brought from the leaves, pass- ing at first from cell to cell by osmosis, then in the sap by way of the bast tubes. In the root or tuber the sugar passes from the vessels to the wood or bark cells by osmosis, and is then converted into Fig. 26. Starch in and darkness light During the daytime the plant manufactures carbohydrate in the leaves, receiving a steady supply of water from the soil. In the dark the starch is changed into sugar and there is a stream of
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