i88 THE PHYSIOLOGY OF PLANTS 



ing one to which on the other side has been removed. The 

 two smaller bundles are of no importance for the success of the 

 operation, but the large median one is of great consequence. 

 It is the small protuberance which must be present on the 

 inside of the bud, as every operator knows, if the bud is to 

 develop. If its place is taken by a small depression, then the 

 vascular bundle {gl) belonging to the bud, and which has to 

 form the woody cylinder of the new shoot, has remained 

 attached to the parent plant. The bud then is represented 

 by a hollow cap, which will not develop any further, even if 

 the wound should heal up. 



The union of tissues takes place most favoui-ably if a layer 

 of callus is formed over the entire inner surface of the scion, 

 as is shown in the figure. The cambium zone lying beneath 

 the bast fibres (h) has formed new cells most profusely, as is 

 shown by the projecting group of cells at z. The cambium 

 layer of the scion {E, c) unites later on with that of the stock 

 (cc), and thus a continuous cambium cylinder once more exists 

 round the stem, and the scion appears inserted in the tissues 

 concerned with the normal nutrition of the stem. 



The method of union of the tissues which takes place after 

 a successful operation we need not describe minutely, for we 

 know how an obliquely cut branch becomes closed in by callus. 

 The cambium layer produces at first soft callus- like layers, 

 which afterwards become hard and cover in the exposed 

 woody tissues. The scion behaves like a cutting, taking the 

 material necessary for its callus formation from the reserve 

 food material which is stored up in its tissues. The stock, 

 which is cut off obliquely above the point at which the bud- 

 ding has been effected, draws the material necessary for closing 

 this cut from the surrounding cells, the cut having been made 

 near to a bud which will soon grow out. The shoot produced 

 by this bud will soon form new plastic matter through the 

 assimilating energy of its own leaves, and the cut will soon be 

 completely healed over. 



But the cut surfaces of scion and stock are in close juxta- 

 position ; the callus tissues formed by them must therefore 

 very soon meet and press one upon the other. The effect of 

 this pressure is to cause the fusion of the callus cells of scion and 



