In gentian, senega, symphytuns, lovage, parsley, inula, echinacea, angelica, burdock, and chicory no crystals of any kind occur. Root hairs occur in cross-sections of sarsaparilla root and false unicorn, but with these exceptions: root hairs do not occur on roots, because the younger part of the root with root hairs is not removed from the soil when the drug is collected. In sarsaparilla root there are several layers of hypodermal cells; in most roots there are no hypodermal cells. In the non-woody roots or the roots of herbs the parenchyma cells form the greater part of the tissues of the root. In ruellia root are stone cells; in spigelia root and many other roots there are no stone cells. In ruellia root are bast fibres; in spigelia, gentian, ipecac, chicory, dandelion, symphytum, and lovage no bast fibres occur. In all the woody roots there is a periderm consisting of typical cork cells, as in black haw; or stone cells, as in asclepias; or of a mixture of lifeless parenchyma, medullary rays, etc., as in Oregon grape root. Woody roots have a phellogen layer which is absent in the non-woody roots. The numbers of layers of cortical parenchyma differ in the same root according to its age, but for a given root there is a normal variation. The number of layers of cortical parenchyma in proportion to other cells is less in woody roots. In woody roots there is no endodermis. The cambium in these cases shows clearly between the phloem and the xylem part of the fibro-vascular bundle. In woody roots the wood fibres are well developed and form a large part of the root, and the medullary rays have pitted side and end walls. The description given above of ruellia root is not typical of all roots, but the structure represents the greater number of the elements that it is possible to find in a root. In many roots, for instance, there are no stone cells, in others no epidermis and no endodermis. In asclepias, aconite, and calumba stone cells occur. In symphytum, chicory, dandelion, burdock, elecampane, pyre thrum, gentian, and senega no stone cells occur. In aconite, althea, asclepias, belladonna, bryonia, columba, ipecac, jalap, krameria, sarsaparilla, scamony, stillingea, and rumex are characteristic starch grains. Symphytum, chicory, dandelion, burdock, elecampane, and pyrethrum contain inulin, but no starch. In saponaria, gentian, and senega neither starch nor inulin occurs. When studying roots the nature of the epidermis or the periderm must be considered, as also the number of layers of cortical parenchyma; the occurrence, distribution, and amount of stone cells when present; the presence or absence of the endodermis; the occurrence and structure of bast fibres when present; the nature of the cambium cells; the width and structure of the medullary rays, the size of the wood fibres and wood parenchyma, and the nature of the cell contents and the arrangement of the fibro-vascular bundle. CHAPTER II