130 



LETTERS ON TREES. 



from the other by the persistent stems and roots of 

 the intervening fifty years' plants. Now, in order to 

 connect them, or rather in order to bring the base of 

 the root into direct relation with the base of the shoot, 

 the expedient of a Cambium- layer is resorted to ; and 

 in striking accordance with the general analogy of the 

 seedling, the tissues into which that layer is trans- 

 formed are identically of the same nature with the 

 root. Thus is the root hfted up, as it were, to the 

 base of the shoot or stem. 



13. It will perhaps enable you the better to under- 

 stand what I have now said, if I observe that there is 

 no natural line of demarcation, and, in point of fact, 

 no structural difference between the woody tissue 

 above-ground, forming what is called the trunks or 

 wood proper, and the woody tissue under-ground, 

 forming what is called the root; and that if we are 

 to adhere strictly to the proper meaning of the terms 

 stem and root^ we must restrict the one to those parts 

 of the mass above-ground which have, year by year, 

 actually grown and risen upivards^ and the other to 

 those parts of the mass under-ground which have 

 actually grown and crept downwards. We should 

 thus have nothing more than the bare skeleton repre- 

 sented in the vertical line of Figure 17, — the parts 

 marked 1, 2, 3, being the stems, and those marked 

 1', 2^ 3', being the roots, — while the side parts, marked 



a, hb, and a^a', 6^6', which represent the woody 



