98 THE OAK 
CHAPTER VIII 
THE TREE—ITS SHOOT-SYSTEM 
WHEN we cut into an old branch or stem of the oak 
(fig. 26), it is at once obvious that considerable changes 
have been produced since it was a twig or young shoot- 
axis, such as exists in the young plant. Of these changes 
the two following are the most conspicuous. ‘The pith, 
instead of being surrounded by a cylinder of small vascu- 
lar cords, the diameter of which hardly exceeds its own, 
as was the case in the one-year-old shoot-axis (fig. 9), is 
now a mere speck in the middle of a huge mass of wood 
many hundreds of times as broad as itself, and the cam- 
bium cylinder which was developed, as we saw, in the pri- 
mary vascular bundles, is now a large (though still thin) 
layer encircling this huge wood mass. Again, in place of 
a delicate epidermis surrounding a soft, green, cellular 
cortex, as we had in the young stem, there is here a hard, 
brown, rugged bark, splitting off in thick ridges on the 
outside. 
The two chief series of change may be inferred from 
comparing the two conditions, and taking into conside- 
ration all we have learnt so far. The pithis the same 
