. Essentials of biology presented in problems. Biology. 122 LEAVES AND THEIR WORK The chloroplasts, hy means of the energy received from the sun, manu- facture starch out of certain raw materials. These raw materials are soil water, which is passed up through the bundles of tubes into the veins of the leaf from the roots, and carbon dioxide, which is taken in through the stomata or pores, which dot the under surface of the leaf. Light and Air necessary for Starch-Making. — If we pin strips of black cloth, such as alpaca, over some of the leaves of a growing geranium, place the plant in a sunny
. Essentials of biology presented in problems. Biology. 122 LEAVES AND THEIR WORK The chloroplasts, hy means of the energy received from the sun, manu- facture starch out of certain raw materials. These raw materials are soil water, which is passed up through the bundles of tubes into the veins of the leaf from the roots, and carbon dioxide, which is taken in through the stomata or pores, which dot the under surface of the leaf. Light and Air necessary for Starch-Making. — If we pin strips of black cloth, such as alpaca, over some of the leaves of a growing geranium, place the plant in a sunny window for two or three days, and then remove some of the covered leaves after a day of bright simlight, we find after ex- tracting the chlorophyll with wood alcohol (because the chlorophyll covers up the contents of the cells) that starch is present only in the portions of the leaves exposed to sunlight. From this experiment we infer that the sun has something to do with starch- making in a leaf. The ne- cessity of air for starch- making may also easily be proved, for the parts of leaves covered with vaseline will be found to contain no starch, while parts of the leaf unvaselined but exposed to the sun and air contain starch. Air is necessary for the process of starch-making in a leaf, not only because carbon dioxide gas is absorbed (there are from three to four parts in ten thousand present in the atmosphere), but also because the protoplasm of the leaf is alive and must have oxygen. This it takes from the air around it. Comparison of Starch-Making and Milling. — The manufacture of starch by the green leaf is not easily understood. The process has been compared to the milling of grain. In this case the mill is the green part of the leaf. The sun furnishes the motive power, the chloroplasts constitute the machinery, and soil water and carbon dioxide are the raw products taken into the mill. The manufactured. Starchless areas in leaves caused by excluding sunlight by means
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectbiology, bookyear1911
