38 UNIVERSITY OF CALIFORNIA. 



ANATOMY AND PHYSIOLOGY OF THE GRAFT. 



(a) The Tissue of the Joint. On the lower section of a graft pruned 

 to one or two eyes/and placed in appropriate conditions as to heat and 

 moisture, there will appear small protuberances of tissue, called callus, 

 on the inner edges or lips of the cut or section. (Just as at the base of 

 all cuttings. See Fig. 1.) These protuberances are but gatherings of 

 cicatricial tissue. They are all the more numerous and developed as 

 they are nearer the base of the section; and on an obliquely-cut graft or 

 scion (as is cut for an " English graft," see Figs. 2, 3, and 4), it is at the 

 lower extremity of the wedge that they first appear. They are destined 

 to cover the wound made by the section, and to shelter it from exterior influ- 

 ences, such as those resulting from rots, etc., by an envelope of cork with 

 which the living parts of the cane (the generating layer, liber, bark, 

 etc.) are covered. The juxtaposition of a corresponding section (that of 

 the subject or stock) alters the destination of the callus. The wood itself 

 has no influence whatever in the formation of the cicatricial tissue; it re- 

 mains just the same as it was at the moment of grafting. Hence the better 

 joints are made without too great an amount of wood being inclosed; the 

 wood being useful only for stiffness. Too much or too little wood is 

 equally bad. A certain amount is necessary to give bark enough to 

 form callus. The principal part in the formation of the callus devolves 

 on the cambium or generating layer. The mechanism of this forma- 

 tion is somewhat as follows: The cells of the scion that are in immediate 

 contact at the surface of the section, and which belong to the regions 

 constituting the generating layer or inner bark, become more active;, 

 they subdivide, multiply, and become prolonged in a direction perpen- 

 dicular (or nearly so) to the surface of the cut. The cells of the soft 

 bast become transformed into still softer cells, the walls of which are 

 thin and non-lignified; they keep on subdividing and multiplying, and, 

 united to those that are the tissues of those resulting from the activity 

 of> the cambium layer, they constitute the small bumps of the cicatricial 

 tissue. Soon the exterior cells, that is to say the oldest, become suberi- 

 fied (or changed into cork), and in one or two layers they form the pro- 

 tecting envelope of cork, more or less resistant, which incloses completely 

 each protuberance, and which becomes attached, sometimes, to the cork 

 envelope of the cane. On the superior section of the canes the same 

 phenomena occur, but they seem to be less distinct and take place much 

 later than is the case with those on the graft itself. This is because the 

 cane (as is the case with the entire vine) has no tendency whatever to 

 cover or protect the wounds made on its superior extremities. The 

 terminal section of the cane never covers itself with callus. The surface 

 of the cut dries out to a varying distance, its channels become clogged 

 with gum, etc., but never close up with living tissue. Every one has 

 noticed that cuttings stratified in cool sand or soil form callus, especially 

 at the lower end of the cane, and only in most exceptional cases is any 

 callus found on the upper end of the cane, and even then this is because 

 of the juxtaposition of another section of cane. 



If a longitudinal section on a cane is made, the cicatricial tissue 

 forms at first on the lateral edges, and scarcely at all on the transverse 

 section. Finally, the cicatricial tissue forms in greater abundance near 

 an eye or bud than near the middle of the internode. It is the pro- 

 tuberances of the cicatricial tissue on the graft and stock placed in con- 



