PROPAGATION. 



237 



tissue; when exposed to the air it evaporates, 

 and its residuum, if any, is dead matter. Addi- 

 tional organized substance is only formed, as 

 above stated, at the circular line which traces 

 the limits between the wood and inner bark. 

 There it may be frequently observed projecting 

 above the level of the section of the stem, and 

 thus rendering evident the seat of organization, 

 where nascent tissues readily unite when brought 

 in contact with similar tissues in a young and 

 active state. This constitutes the fundamental 

 principle of grafting. 



With regard to the cutting intended for the 

 scion, if it is cut off whilst its buds are but little 

 expanded, and its lower end be inserted in the 

 earth, cellular substance will protrude from that 

 end, as the warmth of the season expands the 

 sap, stimulates the buds, and excites the vital 

 action of the tissues. 



Now, if the cellular substance thrown up from 

 the cross-cut stem, and that thrown down by 

 the cutting, could meet each other before the air 

 formed a sort of skin on their respective surfaces, 

 they would coalesce and unite. Such a union, 

 however, would be very insecure, for it is difficult 

 to fix firmly together two pieces of any substance 

 end to end. The scion in this case would derive 

 no mechanical support from the stock to keep it 

 in an upright position; and it would be very 

 liable to be displaced before the cellular substance 

 above mentioned could acquire a sufficiently 

 woody nature to enable it to resist the slightest 

 disturbing force. 



If in the young stem, represented by fig. 297, 

 the edge of a sharp knife be inserted at a, and 

 with one straight sloping cut brought out at b; 

 and if the parts be again joined exactly, ties at 

 c and d will hold them together so that they 

 would not be readily displaced. The ascending- 

 sap, interrupted by the section a b, will not 

 accumulate at i, but will pass along by the inner 

 bark of the section between a and b, and will 

 there meet with the tissue descending from the 

 upper part a b i, which may be termed the scion. 

 Presuming that the parts are very exactly fitted, 

 a most perfect example of grafting will be ob- 

 tained; like parts will be everywhere joined to 

 like, and the whole will be in the best possible 

 position for uniting; the outer barks will coin- 

 cide perfectly, so will the inner barks, and every 

 part of the wood will be brought in contact 

 with its counterpart. It is not, however, to the 

 junction of the outer barks, nor on that of the 

 woods, however exact, that the success of the 

 operation is attributable, but it is on the junc- 

 tion of the inner barks that union depends. This 



TJ-^ 



Fig. 297. -Grafting. 



is the leading principle in all the modes of 

 grafting, and they may be infinitely varied, 

 provided that principle be kept in view. Strictly 

 speaking, the vital union is not effected by the 

 contact of the portions of inner bark, for it, like 

 the outer bark, is a part already formed, whereas 

 the union takes place in con- 

 sequence of the contact of tissues 

 that are in & forming state; such 

 tissues are formed by the cells 

 of the cambium, which lies be- 

 tween the surface of the albur- 

 num and the inner bark ; but the 

 latter is a convenient term to use, 

 because it is generally known; 

 and if two portions of inner bark 

 be joined edge to edge, the sub- 

 stance immediately below them 

 will also be in contact. If we 

 take a piece of clean-grown Wil- 

 low branch in spring, when the 

 sap is in motion, and beat it a 

 little, an entire cylinder of bark 

 may easily be taken from the 

 wood, the latter exhibiting a smooth, slippery 

 surface, as if it had been rubbed with tallow 

 or thin gum. The inside of the cylinder of 

 bark will be found coated with a similar sub- 

 stance. If we take a piece of older wood, with 

 bark as much as J inch thick, dead, rugged, 

 and corky on the outside, yet on removal the 

 internal surface of the wood beneath it will be 

 found smooth, and lubricated with the organiz- 

 ing sap. It is the place where this forms a thin 

 semi-fluid layer that should be joined in grafting, 

 and this will be the case if the inner barks are 

 placed in contact. 



We have supposed fig. 297 to represent a 

 plant; let us now suppose that the stock k d e is 

 a Quince, and that the scion a b i is a Pear shoot 

 well joined. If so, all other circumstances being 

 favourable, a union will take place, and the Pear 

 shoot will grow into a tree, fed by the roots of 

 the Quince ; whilst the latter will add to its bulk 

 by means of sap elaborated by the leaves of the 

 Pear. But whilst this takes place, whatever 

 wood is added to the Quince side of the line a b 

 will be Quince, and that on the Pear side of the 

 same line will be Pear. If the bud e should be 

 allowed to push, it would produce a Quince 

 shoot, although the stem opposite to it chiefly 

 consists of Pear wood ; and, on the contrary, the 

 bud / would give rise to a Pear shoot, although 

 backed by Quince wood. The stock may modify 

 the graft, just as different soils will modify the 

 growth of plants that derive their nourishment 



