PROP A GA Tl ON B Y GRA FT ING, ETC. 243 



operate, and as the scion cannot absorb the sap of the stock, the grafl 

 does not succeed. 



The conditions essential to the success of the graft are the exact 

 coincidence of the alburnum and the inner bark of the scion with 

 those of the stock. The graft is effected in two forms : that of a cutting 

 or scion, which consists of wood and bark with buds (as in grafting 

 and inarching), and that of a bud, which consists of a shield of bark, 

 containing a bud or buds, but deprived of its wood, as in budding. 

 In the case of the scion it is essential to success that its alburnum 

 coincide exactly with that of the stock ; and in the case of the bud it 

 is essential that the disk of bark to which it is attached should be inti- 

 mately joined to the alburnum of the stock by being placed over it, 

 and gently pressed against it by means of ligatures. The buds of the 

 scion and of the shield are supplied with sap from the alburnum of 

 the stock, and develop themselves in consequence. As a proof that 

 it is the ascending sap which supplies the nourishment in both cases, 

 the scion and the bud succeed best when the stock is cut over almost 

 immediately above the graft ; and when the scion or the shield are 

 placed immediately over a part of the stock which contained buds. 

 The success of a scion or a bud placed in the intern odia of the stock 

 where no normal buds can exist, will therefore be much less certain 

 than if it were placed on the nodia ; because the vessels which con- 

 ducted the descending sap to the original buds are ready to supply it 

 to those which have taken their place. Hence, in the case of the graft, 

 fig. 193, the stock is cut sloping, and so as to have a bud on or near 

 the upper extremity of it, in order to prevent the stock from dying 

 down behind the graft ; and the section a, against which the scion is 

 to be placed, is made at the lower part of the sloping section, in order 

 to insure abundance of sap at its upper extremity as well as at its 

 lower ; for were there no bud to expend the sap, it would cease to be 

 impelled through that part of the stock, which would consequently die. 

 By the end of August the scion and stock will be united, and the sec- 

 tion at the top of the latter healed over perhaps as far as e ; and if 

 the heel, or part above c, is then cut off, the part will probably be 

 completely healed over by the end of the season. 



Anatomical Analogy. Plants can only be budded or grafted on one 

 another within certain limits, and these depend on the anatomy or organic 

 structure of the tissue, and the physiology or vital functions of the organs 

 of the plant ; but the anatomy of the cellules and the structure of the 

 vessels are so delicate and difficult to observe, that the differences 

 between plants in these respects are not sufficient to enable us to 

 arrive at any practical conclusion from examining their organization, 

 and hence our only guide in this matter hitherto has been experience. 

 From this it is found that as plants of the same natural family have an 

 analogous organization, they alone can be grafted on one another with 

 any prospect of success; though the success of the operation even 

 within this limit will not always be complete, partly, perhaps, from 

 some difference in organic structure, as in the case of the apple 

 and pear, which can only be united for a few years, but chiefly on 



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