CH.ix.] HEALING OF WOUNDS BY OCCLUSION 211 



easily seen, and is of course well known to every 

 gardener and forester. 



If we remove a small branch of several years' growth 

 from an oak, for instance, it will be noticed that on 

 the twigs last formed there is a bud at the axil of 

 every leaf; but on examining the parts developed two 

 or three years previously it is easy to convince our- 

 selves of the existence of certain small scars, above 

 the nearly obliterated leaf-scars, and to see that if a 

 small twig projected from each of these scars the 

 symmetry of the branching might be completed. Now 

 it is certain that buds or twigs were formed at these 

 places, and we know from careful observations that 

 they have been naturally thrown off by a process 

 analogous to the shedding of the leaves ; in other 

 words the oak sheds some of its young branches 

 naturally every year. And many other trees do the 

 same ; for instance, the black poplar, the Scotch pine, 

 Davimara^ &c. ; in some trees, indeed, and notably in 

 the so-called swamp cypress {Taxodiitvi disticJmm) 

 of North America, the habit is so pronounced that it 

 sheds most of its young branches every year. 



But apart from these less obvious causes for the 

 suppression of branches, we notice in the forest that 

 the majority of the trees have lost their lower branches 

 at a much later date, and that in many cases the 



