62 THE ANATOMY OF WOODY PLANTS 



of its cells in contrast to the regularly and radially disposed 

 structures of the secondary xylem which lies just outside the 

 primary region. It is clear from the figure here introduced that 

 the so-called medullary rays which extend from the primary wood 

 outward cannot be properly so designated, since they never come 

 in contact with the pith. The same situation occurs in the stem 



FIG. 45. Longitudinal view of the primary wood of a lepidodendrid. 

 tion in the text. 



Explana- 



of many other extinct fernlike or gymnospermous plants with 

 secondary growth. It is worth while to note, too, in this connec- 

 tion, that in the root of living plants in which the wood undergoes 

 secondary increase its radially disposed bands of storage cells have 

 nothing to do with a pith or medulla. It is accordingly evident 

 from an examination of older and consequently more primitive 

 forms, and likewise from the study of the organization of the con- 

 servative root structure of living groups, that the term medullary 



