. The essentials of botany. Botany. CRYSTALS 15 but in some plants cells are found which contain so-called "ethereal oils," which are not true fats. 26. Crystals. In many plants may be found cells containing crystals. These may be cubical, prismatic, regular or irregular polyhedrons, needles, compound crystals, etc. Sometimes the cells containing them are unchanged but often they are enlarged or of special shape. This is especially the case with the needle- shaped crystals which are called raphids and occur in large bundles in the cen- tral vacuole of rather large, thin-walled cells.
. The essentials of botany. Botany. CRYSTALS 15 but in some plants cells are found which contain so-called "ethereal oils," which are not true fats. 26. Crystals. In many plants may be found cells containing crystals. These may be cubical, prismatic, regular or irregular polyhedrons, needles, compound crystals, etc. Sometimes the cells containing them are unchanged but often they are enlarged or of special shape. This is especially the case with the needle- shaped crystals which are called raphids and occur in large bundles in the cen- tral vacuole of rather large, thin-walled cells. The crystals seem to be formed by the cytoplasm, in which they occa- sionally lie, or more frequently in special small vacuoles in the latter. Eventu- pound,' and needTe- ,1,1 ~ 1. , â ,! shaped crystals. ally they are lound in most cases m the central vacuole in which some of them may have had their origin. 27. Crystals in most plants are composed of calcium oxalate. In some plants calcium carbonate crystals occur, while crystals of still different composition are occasionally found. The purpose of crystals is not clear in all cases but in many cases they are probably the product of the combination of waste substances set free in the course of some of the important chemical pro- cesses of which the cell is constantly the seat. Laboratory Studies, (a) Make a thin section of a potato tuber. Mount in water. Note the large, thin-walled cells packed with numerous ovoid, concentrically marked starch grains. Treat with iodine solution. The starch grains become blue or purple. In very young tubers, where the starch grains are not so large nor so numerous, they may be seen to be enclosed in leucoplasts. (6) Study the different types of starch grains in corn, wheat, rice, oats, Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the
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