ROOTS AND RHIZOMES 231 



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, elecam- 

 pane, 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, dande- 



