PROPAGATION BY GRAFTING. 



323 



the sap of the stock, the graft does not succeed." 

 Mr G. Lindley, after referring to the circum- 

 stance that, in the stems of grafted trees or 

 plants, the cellular tissue is found alive in the 

 liber and medullary rays only, and that it is 

 essential that those parts both in the scion and 

 stock should be brought into contact, proceeds : 

 " In regard to the medullary rays, these are so 

 numerous, and so closely placed, that it is 

 scarcely possible that a portion of one stem 

 should be applied to another, without the me- 

 dullary rays of both touching each other in 

 many points. No care, therefore, is required to 

 insure this, which may be safely left to chance. 

 But in regard to the liber (or bark), as this is 

 confined to a narrow strip in both stock and 

 scion, great care must be taken that they are 

 both placed as exactly in contact with each 

 other as possible, so that the line of separation 

 of the wood and bark should, in both stock and 

 scion, be accurately adjusted. The success of 

 grafting depends very much upon attention to 

 this. But there are other reasons why this ac- 

 curacy in adjusting the line between the bark 

 and wood of the stock and the scion is so im- 

 portant. It is at that part that the roots of the 

 latter pass downwards over the former ; and it is 

 also there that the substance called cambium, 

 which serves as food for the young descending 

 fibres, is secreted. It is obvious that the more 

 accurate the adjustment of the line separating 

 the wood from the bark, the more ready will be 

 the transmission of young fibres from the one 

 to the other ; and that the less the accuracy 

 that may be observed in this respect, the greater 

 the difficulty in this transmission will be. Pro- 

 vided the stock and scion be of exactly the same 

 size, the adjustment can scarcely fail to be ac- 

 curate in the most unskilful hands : it is in the 

 more common case of the scion being much 

 smaller than the stock that this is to be more 

 particularly attended to." Keith's remarks are 

 even more clearly given : he says, " The whole 

 of the art of artificial grafting is founded upon 

 the capacity inherent in plants of uniting toge- 

 ther by the stems in given circumstances and in 

 a given mode. But the natural graft is always 

 effected by means of the union of the liber of 

 the respective stems composing it ; so that the 

 perfection of the art of grafting consists in ap- 

 plying the liber of the graft and stock together 

 in such a manner as will most facilitate their 

 incorporation ; and hence the graft will not 

 succeed, unless the two libers are brought into 

 contact, and closely bound together. Nor will 

 it succeed well, unless the plants engrafted have 

 some natural affinity to one another, as that 

 subsisting between the plum and cherry; in 

 which, and in all other cases, the union is ef- 

 fected by means of a granular and herbaceous 

 substance exuding from between the wood and 

 bark, and binding and cementing together the 

 stock and graft, though not uniting the former 

 layers of wood." 



Knight, in reference to the same subject, 

 says : " It will be necessary that I describe the 

 motion of the sap, as I conceive it to be at the 

 period when grafts are most advantageously in- 

 serted. The graft first begins its efforts to unite 



itself to the stock just at the period when the 

 formation of a new internal layer of bark com- 

 mences in the spring ; and the fluid which ge- 

 nerates this layer of bark, and which also feeds 

 the inserted graft, radiates in every direction 

 from the vicinity of the medulla to the external 

 surface of the alburnum. The graft is of course 

 most advantageously placed when it presents 

 the largest surface to receive such fluid, and 

 when the fluid itself is made to deviate least 

 from its natural course. This takes place most 

 efficiently when a graft of nearly equal size with 

 the stock is divided at its base, and made to 

 stand astride the stock;" as in a variety of 

 saddle-grafting invented by this eminent phy- 

 siologist. 



The principle on which all the operations in 

 grafting, budding, and inarching are founded, 

 according to Loudon, is dependent on the phe- 

 nomena of the union of newly generated tissues, 

 when in the act of being generated. "No union 

 can take place between the parts of plants pre- 

 viously formed, but only when these parts are 

 in the act of forming. Thus two shoots or 

 branches may be selected, and by means of si- 

 milar sections be most accurately joined, and 

 placed under the most favourable circumstances 

 for uniting ; yet when the two are, bound toge- 

 ther, though a union do ultimately take place, 

 not one particle of the existing tissue, at the 

 time of grafting, becomes united with similar 

 tissue brought in contact with it. Close con- 

 tact is all that takes place with regard to these 

 surfaces of the scion and stock, but a vital union 

 only occurs when nascent tissues meet. The 

 alburnums of the 'preceding year never unite. 

 The vital union is formed solely by the coalition 

 of newly generated tissues, thrown out by such 

 parts as have the power of generating them. 

 This power does not exist in the heart-wood, 

 nor in the outer bark, but only in the albur- 

 num, or rather in the substance imbedded be- 

 tween it and the inner bark, constituting the 

 cambium. If the sections are placed against 

 each other so as the inner barks coincide, the 

 scion may perhaps derive an immediate supply 

 of moisture ; but it does so only in a mechani- 

 cal way, and a piece of dry sponge might as 

 truly be said to have formed a connection from 

 its absorbing moisture, in consequence of its 

 being placed on top of a stock, as the scion, 

 that only takes up moisture as above mentioned. 

 When, however, new tissue is formed by the 

 parts of the respective sections, then, when the 

 portions so formed protrude so as to meet, they 

 immediately coalesce, forming a connecting chain 

 of vessels between the buds of the scion and the 

 roots of the stock. If an old grafted tree is cut 

 down, and all the wood cut away to the origi- 

 nal portions which existed at the time of graft- 

 ing, it will be found that the sections made by 

 the grafting-knife are only mechanically pressed 

 together, and may be easily taken asunder. 

 Instances frequently occur of the inner bark of 

 the scion being placed out of contact with that 

 of the stock, and a union nevertheless ensues ; 

 but this takes place in consequence of the cel- 

 lular substance protruding from the respective 

 alburnums over the surface of the old wood, 



