i84 THE MICROSCOPE. 



which is of a pale pink color. The remainder of the roots is com- 

 posed of white medullary matter, perforated by numerous white 

 longitudinal tubes or ducts, disposed more thickly in concentric 

 circles about the fortieth of an inch apart, or forming a single circle. 

 Radiating from these are delicate medullary rays. When gathered 

 in the spring or early summer, the center is pierced by a light pith 

 or a small cavity. The root when dry is brittle, and snaps readily, 

 giving a clear, smooth fracture. As found in the market 

 there are few, if any, fibers attached, although when fresh 

 the root is well supplied with secondary roots, but as they are very 

 brittle when dry, they do not long remain attached." Its micro- 

 scopical characters are: First, an epidermis of a single row of cells 

 which adheres but loosely to the root; next, a layer of cork varying 

 from four to seven cells in thickness in the specimens examined, 

 the outer rows of which have strongly thickened walls, the inner, 

 less so, and constituting a layer of cork cambium, or meristera. 

 These cells are separated by a tolerably well defined boundary from 

 the inner cortical tissue which occupies in general about one-half 

 the diameter of the root. The cells composing this structure are in 

 the outer portion of the zone, quite irregular in shape and sire, 

 assuming greater regularity, and decreasing somewhat in size to- 

 ward the center, where they approximate to a spherical form. Large 

 laticiferous ducts are found in abundance in this proportion of the 

 root and the cells of this tissue are generally well filled with starch 

 granules, and when fresh, protoplasm. This zone is limited, inte- 

 riorally, by a narrow line of cambium, the cells of which are exceed- 

 ingly difficult to distinguish after the specimen has been dried, and 

 this in turn is succeeded by the medullary sheath, or woody tissue 

 of the root, which, with the exception of a few cells of the semi- 

 diameter of the root. The cells of this tissue are lignified (or 

 woody), and it is composed of three histological elements, compris- 

 ing large dotted ducts, medullary rays, and prosenchyma. The 

 dotted ducts are numerous and plainly visible to the naked eye, but 

 otherwise present no peculiarity. The medullary rays, springing 

 from the central pith and from the annular rings, extend plainly half 

 or two-thirds through the inner bark, where they loose themselves 

 in the general tissue, and are composed, transversely, of one, and in 

 their vertical direction of an indefinite, number, while the medullary 

 cells are, in the transverse section of the ray, elongated, and verti- 



