618 PHYSIOLOGY. 



out the whole of the foliage of the plant. The same phenomenon has "been 

 witnessed repeatedly in the case of variegated kinds of Abutilon. If a 

 variegated scion of A. TJiomsoni be placed on a green-leaved stock, the 

 new leaves pushed out from the latter become also variegated. If a green 

 scion be placed on a stock of the variegated Abutilon, the new leaves of 

 the scion become variegated. Further, if the variegated scion be removed 

 from the green-leaved stock, the latter no longer produces variegated, but 

 only green leaves. A still more striking phenomenon is the production of 

 a hybrid Laburnum, by grafting Cystisus purpurem upon the common 

 Laburnum. Many such cases are now authenticated, and will be referred 

 to under the head of Hybridization. 



Budding consists in attaching the bud of one tree upon the developing 

 wood of another. For this purpose the bud is removed from its parent 

 with a slip of the bark surrounding it, bearing on its inside a portion of 

 the_ cambium-tissue existing at the line of junction of the innermost 

 region of the bark with the youngest wood; this is applied upon the 

 surface of a portion of the cambium-layer of the stock, exposed by slitting 

 its bark and turning it back so as to form a kind of pocket. The slip of 

 bark is inserted into this, so as to bring the cambium of bud and stock 

 into complete contact, and the bark of the stock is then carefully bound 

 down over the wound with bandages of bast, tape, &c. The organizing 

 force resident in the cells of the cambium of the two portions causes them 

 to grow firmly together. 



In Grafting, a shoot instead of a bud is attached to the stock ; and 

 this is commonly effected by cutting off the head of the stock (or a branch 

 of sufficient growth) with an oblique surface, or with a deep notch offer- 

 ing more than one oblique surface ; the bottom of the shoot or graft is 

 pared so as to fit accurately on the oblique surfaces, and in this way con- 

 siderable tracts of the cambium-tissue and young wood are brought into 

 contact their ceUs, however, being partly end to end here, instead of side 

 by side as in budding. Union of the growing region takes place exactly 

 as in the former case. Grafting is usually practised with young woody 

 structures ; but it is also successfully applied to herbaceous plants with 

 careful management ; and some Grasses even admit of being grafted on 

 each other, although the operation is generally confined to Dicotyledonous 

 plants. 



What is termed Inarching, or " grafting by approach," may be com- 

 pared to layering (p. 617) : in this modification of the process, the scion is 

 brought into union with the stock by bending over or otherwise, without 

 being detached from its own stem, and the separation is not made until 

 the scion has " taken " on its foster-parent, &c. 



It was at one time imagined that the annual layers of wood of Dico- 

 tyledonous stems grew down absolutely and mechanically from the buds, 

 of which they were said to represent the roots. It was thought also 

 that, in the case of grafts, the scions sent down woody structure over the 

 old wood of the stock, so as at length to enclose it. From the description 

 given before of the horizontal development of the cambium-layer of Dico- 

 tyledons, it will be seen that such notions are devoid of * all ground. 

 Merely fluid matters pass up and down in the cambium and bark, and the 

 only reciprocal influence of stock and scion depends on the respective 

 activities of roots and foliage. 



