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, 2/3 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.