. Botany, an elementary text for schools. Botany. 248 CONTENTS AND PEODUCTS OF CELLS. 391. Starch grains., a, potato; 6,poinsettia c, rice. abundant of the solid products of the cell. Starch grains have a definite form for each group of plants, and groups can be determined by the form of their starch grains. Detection of adulteration of various products containing starch is accomplished by the aid of the microscope. In potato starch the grains are ovate, with a "nucleus" near one end, as shown in Fig. 391. In poinsettia they are dumb- bell-shaped, with two nuclei (Fig. 391). In corn
. Botany, an elementary text for schools. Botany. 248 CONTENTS AND PEODUCTS OF CELLS. 391. Starch grains., a, potato; 6,poinsettia c, rice. abundant of the solid products of the cell. Starch grains have a definite form for each group of plants, and groups can be determined by the form of their starch grains. Detection of adulteration of various products containing starch is accomplished by the aid of the microscope. In potato starch the grains are ovate, with a "nucleus" near one end, as shown in Fig. 391. In poinsettia they are dumb- bell-shaped, with two nuclei (Fig. 391). In corn they have equal diameters, with radial fissures. In Egyptian lotus they are forked or branched. So far as known all starch grains are marked with rings, giving a striated appearance, due to the difference in density of the layers. When all water is driven out of the starch the rings disappear. The layers are more or less concentric, and are formed about a starch nucleus. 399. Starch grains may be simple, as found in potato, wheat, arrow-root, corn, and many others; or they may be in groups called compound grains, as in oats, rice (Fig. 391), and many of the grasses. 400. Starch may be found in all parts of the plant. It is first formed in presence of chlorophyll, mostly in the leaves, and from there it is carried to some other part of the plant, as to the roots or tubers, to be stored or to be used. When found in the presence of chlorophyll it is called transitory starch, because it is soon converted into liquid compounds to be transported to other parts of the plant. When deposited for future use, as in twigs and tubers, it is stored starch. 401. The composition of starch is in the proportion of CeHioO.'j. The grains are insoluble in cold water, but by saliva they are changed to sugars, which are soluble. Great heat converts them into dextrine, which is soluble in Please note that these images are extracted from scanned page images that may have been digitally enhanced
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