98 THE OAK 



CHAPTER Yin 



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 pith is the same 



