I.] GENERAL CHARACTERS AND STRUCTURE. 15 



those cells of the cambium which are divided off on 

 the outer side of the cylinder (they are always fewer 

 in number) are gradually transformed into elements 

 of the cortex, and many of them finally enter into 

 the composition of the bark proper. 



Now and again, but much more rarely, a radial row 

 of cambial cells which, from their position, it would 

 appear should be converted into tracheides of the 

 wood, alter their destiny, so to speak, and become the 

 originators of a new medullary ray. But I must pass 

 over these and some other minor peculiarities, and 

 refer to the illustrations for further details. 



If now, instead of a log of deal, or coniferous wood, 

 we direct attention to the timber of a dicotyledonous 

 tree, such as the oak, ash, beech, chestnut, poplar, &c., 

 the differences in detail will be found to be not very 

 great in relation to the broad features here under 

 consideration. Turning again to Fig. I, it would be 

 possible to select a cut log of any of these timbers 

 which presented all the salient characters there exhi- 

 bited. The " bark " would present external differences 

 in detail such as in roughness, colour, thickness, &c. 

 but it could still be described, as before, as a more 

 or less corky jacket around the whole of the wood : 

 the cut face would show the timber marked by more 

 or less numerous and prominent "annual rings," 



