256 THE STUDY OF TREES. 



of terminal buds of successive years. Or a tree may be 

 marked by having a string tied around beneath the 

 terminal bud of the year, when in due course the correct- 

 ness of this suggestion will be proved. The ring scars are 

 the marks of the bases of the scales which protect the buds 

 through the winter. 



Having verified this, we are now in a position to tell the 

 age of any given section of a twig, provided the ring scars 

 can be recognised. We note also on examining a large 

 twig that there are many buds which remain quite small 

 and do not become branches. Can we suggest their signi- 

 ficance ? 



We may now examine the cut end of the twig. In a 

 section of a twig of the present year's growth, I can distin- 

 guish with the help of a lens the following : 



An outer skin, which is also seen upon the surface 

 (Fig. 130, e). 



A greenish layer, which is soft and easily penetrated by 

 a pin (d). 



A harder layer, which offers distinctly more resistance to 

 the entrance of the pin. It is pale green in colour, 

 and is bounded by a very thin dark line (b, c) . 



A central soft layer intermediate between the other two, 

 somewhat spongy in texture (a). 



This is not, of course, the best method of examination, 

 but if we supplement it by now peeling off the outer layer 

 at the place where it yields easiest, we may be able to 

 understand more readily some things about the twig. We 

 find that separation takes place along the dark green line 

 referred to above. It is easy to tell now from the texture 

 of the cylinder remaining that it consists of wood, and that 

 in the centre of the wood is the soft spongy substance 

 known as pith. We might now profitably compare our 

 section with one of a fairly stout branch when we find that 

 the pith has gone and that the wood here extends to the 

 centre. This is what happens to the pith in woody branches 

 it is crushed out. 



