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 
Fia. 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 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. (Miiller.) 
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 phloém 
H 2 
