GROWTH OF TREES. 349 



of different degrees of goodness. This is evident in the wood itself, 

 and shows itself upon almost every occasion ; for instance, cut a piece 

 of wood across, and look upon the cut end, you will find the inner part 

 of each layer the hardest and most solid to the eye, but the exterior 

 part is porous, and if it be Fir, we find that it is fuller of rosin. The 

 same appearance takes place upon a longitudinal view of each layer. 

 This is not only seen in sound wood, but it is seen most plainly in the 

 decay of wood, for we find that the outer part of each circle or layer is 

 soonest rotten, and becomes hollow while the other stands. 



On the 1st of August I observed that the present summer's growth 

 of a Fir and of a Laburnum had become the external layer of wood of the 

 tree ; and what now came off in the form of bark, was a new layer of 

 wood that had begun to form, which was of a pale green covered by two 

 cuticles, — one, an outer, thin and brown, the other thicker and green. 

 The outer surface of the last layer of wood was of a very pale green, 

 which could be pushed off with one's nail. This new beginning layer 

 of wood, I apprehend, is formed by a second growth, which trees com- 

 monly have. 



In trees, the first shoot or stalk is always better wood than the 

 second, the second better than the third, and so on, even of the same 

 age. Thus, if we compare the first year's growth of a sucker, or that 

 from a seed, with the second year's growth of another sucker, or from 

 a seed, we shall find that the wood of the first year is much heavier and 

 much tougher. 



The stem is always better wood than the branches, even of the same 

 age ; so that the branches upon the whole are the worst of all. Thus 

 if we compare a branch of any given age with the stem of the same age, 

 we shall find a greater difference than between any of the branches. 



The branch from a branch is worse wood than the branch from a 

 stem, and so on ; so that every succeeding year's wood is worse than 

 the preceding. 



Every branch may be reckoned a stem, or a principal, to the shoot 

 it gives off; and in this view it is similar to the stem with its second, 

 third, <fcc. shoots; and it may be reckoned a principal to its own 

 branches, and is always better wood. The reason of this is evident, for 

 the strength or goodness of the wood must be in proportion to what it 

 has to do, or to support. 



The stem has always the strongest wood where it gives off a natural 

 successive branch ; because, there, it has not only to support the tree 

 equally with every other part of the stem, but it has to support the 

 weight, motion, &c. of that branch. 



Both the stem and the branch grow in thickness in proportion to 



