THE ROOT 171 
4, Endodermis, or innermost layer of cells of the cortex, whose 
radial walls are lenticularly thickened. 
5. Pericambium (Pericycle), of a layer of actively growing meri- 
stematic cells, which has the power of producing lateral rootlets. 
ep 
Fic. 103.—Photomicrograph of a transverse section of a California Privet root 
made about 114 inches above the root tip and showing transition structure. The 
epidermis (ef), primary cortex (pc) and endodermis are in the process of sluffing 
off, since cork (ck) has been laid down by the cork cambium (pn) directly beneath 
the endodermis. The cork cambium has also formed several layers of secondary 
cortex (sc) on its inner face. The protophloem ( pp) represented largely by hard bast 
has been pushed out, while a small amount of secondary phloem (sp) represented 
by soft bast has been deposited beneath it by the cambium (c) which now is 
nearly circular in aspect. The protoxylem (px) has been pushed into the center 
by the encroaching secondary xylem (sx) which has been laid down by the cambium 
on its inner face. mr, medullary ray. Highly magnified. 
6. Radial fibro-vascular bundle of five or six primary xylem arms 
alternating with as many primary phloem patches. Note the 
narrow spiral trachez in the xylem patches. 
7. Pith, a small central zone of parenchyma. 
