170 THE DEVELOPMENT OF BRITISH FORESTRY 



marked by a change in the physical structure and 

 chemical constituents of the stem. The cell walls of the 

 wood become hardened or lignified, and the cell sap 

 denser and more sugary, both of which changes enable 

 the shoots of the previous summer to withstand the 

 greatest degree of cold, or the longest spell of cold, 

 drying wind, normally borne by the species. When 

 winter cold sets in before this process is completed the 

 ends of the shoots, which are the least lignified por- 

 tions, are either frost-bitten, or desiccated by wind at low 

 temperatures, according to the prevailing conditions at 

 the time. 



Another feature of woody perennials is the extension or 

 prolongation of their root systems, so that, in course of 

 time, the extremities or growing points of the more 

 vigorous roots are many feet distant from the collar or 

 base of the stem. While a bulb or herbaceous plant, 

 therefore, can be transplanted at ten or twenty years of 

 age — assuming that it lives so long — as easily as it can at 

 one or two years, the difficulty of transplanting woody 

 plants increases with age, and can only be successfully 

 accomplished when special methods are adopted, such as 

 frequent transplanting, root-pruning, etc., so that living 

 and functional roots are attached to the transplanted 

 tree in sufficient numbers to maintain the transpiration 

 current. The above facts are well known to any one who 

 thinks of them. Many persons forget or do not take the 

 trouble to remember them, however, and that must be 

 the only apology for mentioning such elementary points 

 here. 



Successful transplanting may be said to depend in the 

 first instance, therefore, upon the following conditions 

 being fulfilled: — The shoots of the 'plant must he suf- 

 ficiently ivell ripened to enable them to ivithstand the 

 amount of desiccation to ivhich they are subjected after 



