THE TREE ITS SHOOT-SYSTEM. 



99 



pith as before, and it is the cambium cylinder which 

 has moved outwards, as it were, putting in all that 

 solid-looking timber as it did so. The epidermis and 



FIG. 26. Photograph of the transverse section of a log of oak, about one 

 sixth natural size. The cortex and bark are removed, and the outline 

 is bounded by the cambium. The pith appears as a mere dot in the 

 center; the medullary rays radiate from this, and the annual rings 

 (about forty in number) are arranged concentrically around it. A 

 large crack has formed along the plane of a medullary ray as the 

 section dried. (Muller.) 



the cortex of our young stem have disappeared, how- 

 ever, their place being taken by cork and bark. Closer 

 inspection will show that a series of layers of phloem 



