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Test for grape sugar.

A Test for Grape Sugar.—Place in a test tube the substance to be tested and heat it in a little water so as to dissolve the sugar. Add to the fluid twice its bulk of Fehling's solution,[6] which has been previously prepared. Heat the mixture, which should now have a blue color, in the test tube. If grape sugar is present in considerable quantity, the contents of the tube will turn first a greenish, then yellow, and finally a brick-red color. Smaller amounts will show less decided red. No other substance than sugar will give this reaction. If Benedict's test[7] is used, a colored precipitate will appear in the test tube after boiling.

Starch changed to Grape Sugar in the Corn.—That starch is being changed to grape sugar in the germinating corn grain can easily be shown if we cut lengthwise through the embryos of half a dozen grains of corn that have just begun to germinate, place them in a test tube with some Fehling's solution, and heat almost to the boiling point. They will be found to give a reaction showing the presence of sugar along the edge of the cotyledon and between it and the endosperm.

Digestion.—This change of starch to grape sugar in the corn is a process of digestion. If you chew a bit of unsweetened cracker in the mouth for a little time, it will begin to taste sweet, and if the chewed cracker, which we know contains starch, is tested with Fehling's solution, some of the starch will be found to have changed to grape sugar. Here, again, a process of digestion has taken place. In both the corn and in the mouth, the change is brought about by the action of peculiar substances known as digestive ferments, or enzymes. Such substances have the power under certain conditions to change insoluble foods—solids—into soluble substances—liquids. The result is that substances which before digestion would not dissolve in water now will dissolve.

A germinating corn grain. C, cotyledon; H, growing root (hypocotyl); P, growing stem (plumule); S, endosperm; d.s., digested starch; p.r., primary root; s.r., secondary root; r.h., root hairs.

The Action of Diastase on Starch.—The enzyme found in the cotyledon of the corn, which changes starch to grape sugar, is called diastase. It may be separated from the cotyledon and used in the form of a powder.

To a little starch in half a cup of water we add a very little (1 gram) of diastase and put the vessel containing the mixture in a warm place, where the temperature will remain nearly constant at about 98° Fahrenheit. On testing part of the contents at the end of half an hour, and the remainder the next morning, for starch and for grape sugar, we find from the morning test that the starch has been almost completely changed to grape sugar. Starch and warm water alone under similar conditions will not react to the test for grape sugar.

Digestion has the Same Purpose in Plants and Animals.—In our own bodies we know that solid foods taken into the mouth are broken up by the teeth and moistened by saliva. If we could follow that food, we would find that eventually it became part of the blood. It was made soluble by digestion, and in a liquid form was able to reach the blood. Once a part of the body, the food is used either to release energy or to build up the body.

Summary.—We have seen: 1. That seeds, in order to grow, must possess a food supply either in or around their bodies.

2. That this food supply must be oxidized before energy is released.

3. That in cases where the food is not stored at the point where it is to be oxidized the food must be digested so that it may be transported from one part to another in the same plant.

The life processes of plants and animals, so far, may be considered as alike; they both feed, breathe (oxidize their food), do work, and grow.

[3] Iodine solution is made by simply adding a few crystals of the element iodine to 95 per cent alcohol; or, better, take by weight 1 gram of iodine crystals,⅔ gram of iodide of potassium, and dilute to a dark brown color in weak alcohol (35 per cent) or distilled water.

[4] Other tests somewhat more reliable, but much more delicate, are the biuret test and test with Millon's reagent.

[5] Limewater can be made by shaking up a piece of quicklime the size of your fist in about two quarts of water. Filter or strain the limewater into bottles and it is ready for use.

[6] and [7] Directions for making these solutions will be found in Hunter's Laboratory Problems in Civic Biology.

Reference Books

elementary

Hunter, Laboratory Problems in Civic Biology. American Book Company.

Andrews, A Practical Course in Botany, pages 1–21. American Book Company.

Atkinson, First Studies of Plant Life, Chap. XXX. Ginn and Company.

Bailey, Botany, Chaps. XX, XXX. The Macmillan Company.

Beal, Seed Dispersal. Ginn and Company.

Bergen and Davis, Principles of Botany, Chaps. XX, XXX. Ginn and Company.

Coulter, Plant Life and Plant Uses. American Book Company.

Dana, Plants and their Children. American Book Company.

Mayne and Hatch, High School Agriculture. American Book Company.

Lubbock, Flowers, Fruits, and Leaves. The Macmillan Company.

Newell, Reader in Botany, pages 24–49. Ginn and Company.

Sharpe, A Laboratory Manual in Biology, pages 55–65. American Book Company.

advanced

Bailey, The Evolution of our Native Fruits. The Macmillan Company.

Bailey, Plant Breeding. The Macmillan Company.

Coulter, Barnes, and Cowles, A Textbook of Botany, Vol. I. American Book Company.

De Candolle, Origin of Cultivated Plants. D. Appleton and Company.

Duggar, Plant Physiology. The Macmillan Company.

Farmers' Bulletins, Nos. 78, 86, 225, 344. U. S. Department of Agriculture.

Hodge, Nature Study and Life, Chaps. X, XX. Ginn and Company.

Kerner (translated by Oliver), Natural History of Plants. Henry Holt and Company, 4 vols. Vol. II, Part 2.

Sargent, Corn Plants. Houghton, Mifflin, and Company.