PROPAGATION. 



251 



varieties by what is termed "graft hybridisation." 

 Herbaceous grafting of resinous trees is also per- 

 formed, when the shoots are making their growth 

 and still quite soft. The stems of these exogens, 

 otherwise dicotyledonous plants, and gymnosperms, 

 such as the Conifers, may be roughly divided into 

 pith, wood, and bark. Between the wood and the 

 bark is a thin layer of tissue, consisting of thin- 

 walled cells in their primitive, simple, undifferen- 

 tiated condition, filled with formative or constructive 

 material. These, in plants that periodically increase 

 in bulk by additional concentric rings, retain, as long 

 as the life of the plant continues, their power of 

 growth and division, adding at each separate growth 

 fresh wood to the inside, and fresh bark to the outside. 

 Hence, the youngest wood is on the outside or cir- 

 cumference of the stem, while the youngest bark is 

 on the inside of this tissue, and next to the formative 

 layer just mentioned, and best known as cambium. 



Endogens or monocotyledons are differently con- 

 structed; their stems are not separable into pith, 

 wood, and bark. The, external surface of some 

 Palms and tree Liliacece appears to be invested with 

 a layer of bark, but this roughened exterior is 

 merely caused by the degradation of the ordinary 

 tissue of the stems. The outer or circumferential 

 tissues are usually much harder than the inner, and 

 this gave rise to the opinion formerly entertained 

 that the oldest wood was outermost, and that growth 

 proceeded from the circumference towards the centre ; 

 hence, the application of the term " endogen." This, 

 however, is no longer believed. The wood, instead 

 of forming annual concentric rings, forms isolated 

 fibro- vascular bundles, scattered through the ground 

 tissue, while the hardness of the outer portion of the 

 stem is caused by a denser arrangement of the re- 

 spective bundles there. 



Now, the fundamental principle of the whole sys- 

 tem of grafting consists in placing and keeping the 

 cambium layer of the two cut surfaces so closely 

 together as to favour their union when they make 

 fresh growth. The cut surfaces of the wood merely 

 remain in contact, and no union takes place beyond 

 the cambium. There is no cambium layer in en- 

 dogens, and hence the impracticability or greater 

 difficulty of grafting them. 



Various objects are aimed at in grafting, but the 

 main one is simply a practicable, convenient, and 

 profitable means of propagation. Many things are 

 difficult to propagate except by grafting, such as 

 some of the Clematis and Azaleas, and these can be 

 i worked on the roots or stocks of a commoner sort, 

 more readily obtained by other methods. Another 

 important object gained is the modification of the 

 ; scion or graft by the influence of the stock. For 

 instance, in deep heavy soils, it is advantageous to 



cultivate shallow-rooting trees, to avoid the evil 

 effects of a cold, wet bottom. In the case of the Pear, 

 this is managed by grafting on the Quince, which is 

 shallow-rooted, and at the same time a less vigorous 

 grower, thereby exercising a dwarfing influence on 

 the scion. Not only is coarse and excessive woody 

 growth restrained, but an earlier fruiting tendency 

 is induced, resulting frequently in larger, better- 

 coloured fruit. Various other results and modifica- 

 tions are effected by grafting, which will be best 

 noticed under the respective subjects. 



One important point must not be overlooked in 

 the relation of stock to graft. The mere union of 

 plants belonging to different species or genera 

 seldom affects either in any appreciable degree ; so 

 that in the case of a Peach grafted on the Plum, all 

 above the point of union will be Peach-wood, and 

 all below this, Plum-wood. These relations will 

 remain constant, even if tested after any lapse of 

 time. There may be a few remarkable exceptions 

 to this rule, of which Cytisus Adami may be cited 

 as a familiar and well-known example. It is now 

 generally believed to be a graft hybrid, obtained by 

 inserting a bud of C. purpureus on 0. laburnum. 

 The result is an individual intermediate between the 

 two parents, and which occasionally reverts to 

 either parent on different branches of the same tree. 

 In the relations of stock to graft, generally, it will 

 ■ be the cultivator's aim to prevent undergrowth, or 

 suckers from the stock, which, in many cases, would 

 soon obtain the mastery, and overpower or outgrow 

 the weaker scion. This is most important in the 

 case of grafted Roses. 



Modes of Grafting. — The principle of graft- 

 ing, as already mentioned, is invariably the same ; 

 but there are several modifications, more or less 

 adapted for different subjects, or calculated to in- 

 sure expedition as well as efficiency. The most ex- 

 peditious, generally useful, and that most frequently 

 practised in this country, is known as — 



Whip -grafting, or Splice -grafting.— The 



stock and scion may be of equal size, when the 

 most perfect union can be effected; or the former 

 may be of any size or age without materially af- 

 fecting the success of the operation. When the 

 stock and scion are of equal thickness, the former, 

 after being headed down to the intended point, 

 should have a cut made in a sloping direction 

 (Fig. 19). Entering the knife at the lower end 

 of the intended cut face, bring it out on the op- 

 posite side, immediately above a bud if possible. 

 This will help to prevent the thin upper end of the 

 stock dying back. The operator should use a sharp 

 knife only, as the success of the graft is greatly 



