[ 233 ] 



consequence of this process, as an unprotected stan- 

 dard tree ; and the layers from such trees are much 

 more hardy than the layers from myrtles reared with- 

 in doors. 



The arbutus, probably originally from similar 

 cultivation, has become the principal ornament of the 

 lakes of the south of Ireland. It thrives even in bleak 

 mountain situations; and there can be little doubt bu.t 

 that the offspring of this tree inured to a temperate cli- 

 mate might be easily spread in Britain. 



The same principles that apply to the effects of 

 heat and cold will likewise apply to the influence of 

 moisture and dryness. The layers of a tree habitua- 

 ted to a moist soil will die in a dry one: even though 

 such a soil is more favourable to the general growth 

 of the species. And, as was stated page 1 69, trees 

 that have been raised in the centre of woods are soon- 

 er or later destroyed, if exposed hi their adult state to 

 blasts, in consequence of the felling of the surround- 

 ing timber. 



Trees, in all cases, in which they are exposed in 

 high and open situations to the sun, the winds, and 

 the rain, as I just now noticed, become low and ro- 

 bust, exhibiting curved limbs, but never straight and 

 graceful trunks. Shrubs and trees, on the contrary, 

 which are too much sheltered, too much secluded 

 from the sun and wind extend exceedingly in height; 

 but present at the same time slender and feeble 

 branches, their leaves are pale and sickly, and in ex- 

 treme cases they do not bear fruit The exclusion 

 of light alone is sufficient to produce this species of 



H 2 



