PROPAGATION BY GRAFTING, ETC. 



281 



that only takes up moisture as above-mentioned. AVhen, however, new 

 tissue is formed by the parts, &, 6, of the respective sections, and when the 

 portions so formed protrude so as to meet, they immediately coalesce, form- 

 ing a connectmg 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 original portions which existed at the time of grafting, it will 

 be found that the sections similar to a, a, 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 cellular substance protruding from the 

 respective alburnums over the surface of old wood, which it only covers, 

 as soon as the new-formed tissue of stock and scion touch each other, a 

 union is then formed. 



638. The origin of grafting is of the most remote antiquity, but whether 

 it was suggested by the adhesions of the parts of two plants, frequently seen 

 in a state of nature, or by the appearance of one plant growing on another, 

 as in the case of the mistletoe, it is impossible to divine. Theophrastus and 

 other Greek authors mention the graft ; and upwards of twenty modifica- 

 tions of it have been given by the Roman Varro. The principal modern 

 author on the subject is M. Thouin, of Paris, who has described and figured 

 more than a hundred kinds, and INI. Tschudy, of Metz, who was the inven- 

 tor of the art of grafting herbaceous plants, and ligneous plants in an herba- 

 ceous state. The theory of grafting was first given in a lucid manner by 

 the celebrated De Candolle in his *' Physiologie Vegetale" From these works, 

 and our own observations, we shall first treat of what is common to grafting 

 inarching, and budding, and next treat of these modes separately. 



639. The phenomena of grafting are thus explained by De Candolle : — 

 The shoots springing from the buds of the scion are united to the stock 

 by the young growing alburnum, and, once united, they determine the ascent 

 of the sap rising from the stock ; and they elaborate a true or proper juice^ 

 which appears evidently to redescend in the inner bark. This sap appears 

 to be sufficiently homogeneous in plants of the same family — to be, in 

 the course of its passage, absorbed by the growing cellules near which it 

 passes, and each cellule elaborates it according to its nature. The cellules 

 of the alburnum of the plum elaborate the coloured wood of the plum ; 

 those of the alburnum of the almond the coloured wood of the almond. If 

 the descending sap has only an incomplete analogy with the wants of the 

 stock, the latter does not thrive, though the organic union between it and 

 the scion may have taken place ; and if the analogy between the alburnum 

 of the scion and that of the stock is wanting, the organic union does not 

 operate, and as the scion cannot absorb the sap of the stock, the graft does 

 not succeed. In the case of the mistletoe, which may be considered as a 

 natural graft, there is an analogy between the two alburnums, but none 

 between the barks ; whence it follows that, though the mistletoe can very 

 well unite itself with the alburnum of the tree on which it grows, yet the 

 descending sap formed by the bark of the mistletoe does not enter the bark 

 of the tree which bears the parasite, and therefore cannot nourish it. This 

 is the cause of the impoverishment of branches of trees on which the mistletoe 

 has fixed itself, and perhaps the possibility of that parasite living on trees of 

 every natural family, and which possibility M. De Candolle attributes to the 

 identity of the ascending sap. {Phys. Veg., vol. ii., p. 814.) 



