242 



PROPAGATION BY GRAFTING, ETC. 



Fig. 193. 



does so only in a mechanical way, and a piece of dry sponge might as 

 truly be said to have formed a connexion from its absorbing moisture, 

 in consequence of being placed on the top 

 of a stock, as the scion that only takes 

 up moisture as above-mentioned. When, 

 however, new tissue is formed by the parts, 

 b, b, of the respective sections, and when the 

 portions so formed protrude so as to meet, 

 they immediately coalesce, forming a con- 

 necting 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 mechani- 

 cally 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 sub- 

 stance protruding from the respective albur- 

 nums over the surface of old wood, which 

 Scion and stock, to illustrate . , L 



the principle on which they li Onl 7 covers. As soon as the new-formed 

 are united. tissue of stock and scion touch each other, 



a union is then formed. 



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 up- 

 wards of twenty modifications of it have been given by the Roman 

 Varro. 



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 deter- 

 mine the ascent of the sap rising from tlje stock ; and they elaborate 

 a true or proper juice, which appears evidently to re-descend 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 



