To prove that these food stuffs must be digested before they can be used in germinating plants, corn seeds can be tested for starch and for grape sugar, both before and after germination has started.
Starch is insoluble in cold water, and does not pass readily through the absorbing membranes. Therefore it has to be digested (changed to soluble sugars) before the plant can use it.
This digestive change is accomplished by a substance in the seed, called diastase, which acts somewhat like the digestive fluids in our bodies.
If the corn be tested before germination has begun, much starch and little or no sugar will be found. If it be tested in the same ways, after germination has proceeded for a few days, the reverse will be discovered, as most of the stored starch will have been converted into soluble form, sugar, by the diastase in the cotyledon.
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