148 GROWTH OF PLANTS. 



wood of the mother branch, as well as of the trunk, 

 down to the very extremities of the roots. These fibres 

 descending from the bud, meet in their descent with 

 the fibres from other contiguous buds, and these toge- 

 ther form the annual ring of hard wood ; the bark in 

 the same way is increased by bark fibres descending 

 from the buds. The whole of the bark and of the 

 wood in this view are nothing more than the roots of 

 buds. 



It has been supposed that Hales had some opinion 

 similar to this, when he says, <( That it is not easy to 

 conceive how additional ringlets of wood should be 

 formed by a merely horizontal dilatation of the vessels ; 

 but rather by the shooting of the longitudinal fibres, 

 lengthways under the bark, as young fibrous shoots of 

 roots do in the solid earth." However this may be, the 

 opinion is clearly fanciful, as Professor Henslow has 

 justly said. 



Professor Amici says, I perfectly agree with M. 

 Mirbel, that between the bark and the wood .there are 

 successively organised layers, of which one part unites 

 with the pulp wood and acquires its nature, and the 

 others are placed upon the inner bark, augmenting its 

 mass. But we do not yet know the origin of the young 

 tissue, which has been distinguished under the name of 

 pulp tissue. 



These several opinions may all be referred to three 

 general heads. 



I. That growth in diameter is carried on by the 

 annual change of the inner bark into pulp wood, and 

 of pulp wood into hard wood, and by the successive 

 renewal of the inner bark. 



