112 



LETTERS ON TREES. 



He starts, you will observe, from the same point, 

 making the same assumption that I do (Letter I. 6). 

 And after stating how this law applies to several sorts 

 of plants, he goes on to say of trees — 



''In the dicotyledonous class there are enormous trees, 

 whose existence seems to date from before the records of his- 

 tory^ and which, in spite of their antiquity^ are loaded^ in each 

 returning year, with blossom and seed, 



''If we were to view the perennial and woody plants as 

 simple individuals, as such we should be naturally induced to 

 conclude, that unless destroyed by disease or casualties, they 

 were free from the liability to death from old age ; but a due 

 consideration leads us to distinguish ia every perennial and 

 woody plant, the new part which actually lives and grows^ from 

 the old^ which has ceased to grow^ and is dead. 



" I will state this in a broader way. Plants of this nature 

 have two modes of propagating their races : one, by seeds — the 

 other, by a continuous evolution of like parts. In the first case, 

 the seed presents us with an embryo plant, a new and different 

 individual, independent, and unconnected with that from which 

 it derived its existence ; in the second, we are presented with 

 a series of individuals., which issue from the surface the one of 

 the other in an uninterrupted sequence, and in some instances 

 continue permanently united. But whether individuals of this 

 description are produced by seed or b}^ continuous evolution, 

 it is certain that they escape, in neither case, the influence of 

 time ; while, on the other hand, the succession of individuals, 

 or what we may call the race, produced in either of the ways, 

 is as clearly beyond the reach of age^ and will endure until 

 destroyed by some extraneous cause. 



" We will endeavour to show how these general laws apply : 

 — All the parts of the young herbaceous annual are susceptible 

 of enlargement ; the ceUs of the tubes, at first very small, are. 



