THE TKEE 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 out line is bounded by the cambium. 

 The pith appears as a mere dot in the centre ; the medul- 

 lary 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 medul- 

 lary 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 



H 2 



