ROOTS AND RHIZOMES oat 
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, pyrethrum, 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- 
