THE USE OF SHOOTS FOE PROPAGATING 189 



stock, the cambium layers uaiting to form a continuous cam- 

 bium cylinder. The closer the cut surfaces are one to the 

 other, the more rapidly do the cells which are capable of fusion 

 meet, and the more quickly and completely is the union 

 brought about. Hence gardeners have adopted the rule that 

 in all processes of grafting and budding the cambium layers 

 must be brought into contact. This, however, is only then 

 completely possible when the scion and stock are of the same 

 thickness. If this is not the case, we must at all events 

 endeavour to secure that on one side the two cambial layers 

 will meet, so that the scion may from the outset be nourished, 

 and that it may at least receive the water which it needs. 



If the scion becomes attached at one side, at all events, so 

 that it does not suffer from lack of water, it will soon be able 

 to help itself. The growing buds will form such quantities of 

 food matter that it will very soon form large masses of callus, 

 and these will cause a union to take place on those sides which 

 do not fit. This is most frequently seen in the case of cherry- 

 trees which have not been properly ligatured. The scion 

 will in these cases often be found to have an oblique position 

 owing to the fact that on the non- fitting side large masses of 

 callus have been formed which did not at first unite. 



In such cases the advantage of properly binding up the 

 graft is seen ; the callus masses must not be able to push each 

 other away. If the scion cannot give way, the callus layers 

 will, under the action of the pressure, unite. The separating 

 of scion and stock after the operation can be prevented by 

 the so-called tongue grafting or tonguing. 



The fusion of stock and scion takes place with the greatest 

 difficulty in the case of crown grafting. 



The dangerous element here is the wound which is inflicted 

 upon the wild stock, which is either split longitudinally or 

 has at least a wedge-shaped portion of wood removed from its 

 upper end. Now the two cut faces of the wound expose the 

 old wood, which cannot give rise to any healing tissue. The 

 closure of the deep split, therefore, can only be effected by 

 the ingrowing of callus from the peripheral cambium layers. 

 This, however, only very rarely takes place completely ; 

 generally there remain gaps at the centre of the stem, and the 



