208 



APPLICATION OF PRINCIPLES. 



into the main stem, while a small quantity is allowed 

 to rise out of the latter into the former ; the effect of 

 this being to compel the returning sap to organize it- 

 self externally as roots, instead of passing downwards 

 below the bark as wood. The bending back is to 

 assist in this object, by preventing the expenditure of 

 sap in the formation, or rather completion, of leaves ; 

 and the silver sand is to secure the drainage so neces- 

 sary to cuttings. 



In most cases, this is sufficient ; but it must be 

 obvious that the exact manner in which the layering 

 is effected is unimportant, and that it maybe varied 

 according to circumstances. Thus, Mr. James Munro 

 describes a successful method of 

 layering brittle-branched plants 

 by simply slitting the shoot at 

 the bend, and inserting a stone 

 at that place {Gardener 1 a Maga- 

 zine, ix. 302) : and Mr. Knight 

 found that, in cases of difficult 

 rooting, the process is facilitated 

 by ringing the shoot just below 

 the tongue, about midsummer, 

 when the leaves upon the layers 

 had acquired their full growth 

 (ffort. Trans., i. 256) ; by which 

 means he prevented the passage 

 of the returning sap further 

 downwards than the point in- 

 tended for the emission of roots. 

 It will sometimes happen that 



