PLANT ORGANS AND ORGANISMS 131 



cambium. This cork cambium has developed secondary cortex on 

 its inner face. The cambium has assumed a circular aspect. Just 

 beneath the secondary cortex will be found flattened patches of 

 protophloem, and beneath these secondary phloem masses have 



PIG. 64. Photomicrograph of a transverse section of an old portion of 

 California Privet root, showing completed secondary development. Note the 

 prominent medullary rays (mr); cork (ck)\ phellogen (ph~); secondary cortex 

 (between ph and p')\ protophloem (p')\ secondary phloem ( 2 ); cambium (c); 

 secondary xylem (# 2 ); tracheae (/); wood fibers (wf); and protoxylem (#') 



been formed through the activity of the cambium. The cambium 

 has developed new or secondary xylem on its inner face which has 

 pushed the first formed or protoxylem toward the center of the root. 

 (Fig. 63.) 



