192 THE PHYSIOLOGY OF PLANTS 



by scion has become closed by the activity of th,e pith (mk), 

 which has formed a number of rows of callus cells (mc'), which 

 continued to grow at their apex, until they met those produced 

 from the other side of the pith. 



Thus we see all the cavities between the stock and the scion 

 have become completely filled by callus, and as the cambium of 

 both e and c' have fused, we see that crown grafting may be 

 performed, in the case of the Lime, as readily as any other 

 method of improving the stock. 



The healing is also very successful if the scion is not cut 

 into a triangular wedge, but if it is only pared down on either 

 side so that both sides are still covered with cortical tissue. 

 The centre of the split is in this case filled by cortical cells 

 which can form callus tissue to fill up the crack. Crown 

 grafting cannot, however, be entirely neglected. This opera- 

 tion has to be resorted to in the case of old stems, the cortex 

 of which does not easily separate from the woody cylinder, 

 and it is advantageous when grafting on root-stocks (Pceonia 

 arborea, Clematis, Bignonia, (fee). After the discussion of the 

 three chief methods employed for the improvement of wild 

 stock, we may now discuss the advantages of certain modifica- 

 tions of these methods. 



Thus small graft shoots may be inserted into a T-shaped 

 incision into the cortex of the stem. This is most advanta- 

 geous in the late summer. The shoot is then trimmed like 

 an ordinary graft. This method is very advantageous, and 

 generally practised in the spring, as soon as the cortex can 

 be easily separated in the stock. It is of advantage in the 

 case of trained trees in which some branch has been injured, 

 and also in the case of an old stock which is too thick to allow 

 of a bud being introduced into it. This method might be 

 called budding with a shoot. 



If the crown of the old stock is to be preserved, lateral 

 grafting may be practised. In the case of evergreen shrubs 

 (Camelias, Rhododendrons, Azaleas, Conifers, &c.), a last year's 

 shoot still provided with its leaves is used as a scion, and a 

 piece of the stock of similar size is cut away from the side of 

 the stem, so that the wound which is thus caused is covered 

 as completely as possible by the scion. 



