i8 TIMBER AND SOME OF ITS DISEASES. [CHAP. 



generally, of the medullary rays here that is true of 

 those of the pines and firs, &c. 



FIG. 6. A piece of wood from a dicotyledonous tree (beech), supposed to be magni- 

 fied about 100 times. Mr, a medullary ray running across the transverse section : 

 the dark band crossed by this ray is the autumn wood (<*), formed of closely- 

 crowded wood-fibres and tracheides : v, a large vessel in section: others are seen 

 also they are smaller and fewer towards the autumn wood ; a', wood-fibres, of 

 which most of the timber is composed ; tup, wood-parenchyma cells. 



Attention is to be directed to the fact, which is here 

 again evident, that the line of demarcation between 



