401 



GRAFTING. 



GRAFTING. 



4C3 



two or more equidistant readings wishes to examine the divisions, he 

 may get rid of the effect of excentricity thus : Take the mean of the 

 readings at every 10, 20, or 30,and subtract eachreading from the mean. 

 It will be seen whether the differences thus obtained can be represented 

 under the form of a constant quantity + x" x siu. 8, where 6 is reckoned 

 from some definite point. If they can, there is no error of division, 

 and the residual quantities, when the above equation has been satisfied 

 in the best practicable manner, will give some insight into the quality 

 of the divisions. The error which arises from the original circular 

 form changing to an ellipse by a fall or other injury is of the form 

 y" x sin. 2<f>, where ^> is the angle from some definite point of the 

 divisions. Hence two readings at right angles, or three equidistant 

 readings, will compensate each other ; BO that three or more equi- 

 distant readings will destroy the effect of both excentricity and 

 ellipticity. In like manner the effect of any error which obeys a law 

 may be investigated, when the law is known, and also the number of 

 microscopes. Hitherto four or six microscopes seem to have made 

 every circle a well-divided one. 



The mode of reading the parts of larger divisions has been partly 

 explained in the description of the microscope, article CIRCLE [ASTRO- 

 NOMICAL], and will be finished under the head VEHNIEH. 



The principal sources of information on this subject are : ' The 

 Method of Dividing Astronomical Instruments/ by Mr. John Bird. 

 London, 1787. ' Nouvelle Me'thode pour diviner les Instruments de 

 Mathe'matique et d'Astronomie," par M. le Due de Chaulnes, 1/68. 

 ' Description of an Engine for dividing Mathematical Instruments,' by 

 Mr. J. liamsden. London, 1777. Trough ton's Memoir,\' Phil. Trans., 

 1809, p. 105. Graduation, ' Edinburgh Cyclopaedia." This very valu- 

 able article ig by Troughton. ' On the Errors of the Cape Mural 

 Circle,' by Messrs. Sheepshanks and Airy, ' Memoirs Royal Astrono- 

 mical Society,' vol. v., p. 325. ' On the Cape Mural Circle,' by Pro- 

 fessor Henderson, ' Memoirs Royal Astronomical Society, 1 vol. viii., 

 p. 141. ' Description of the Mural Circle of the Armagh Observatory," 

 by Dr. Robinson, ' Memoirs Royal Astronomical Society,' vol. ix., p. 17. 

 ' Report on the Standard Scale of the Royal Astronomical Society,' by 

 Mr. F. Baily, ' Memoirs Royal Astronomical Society," vol. ix., p. 35. 

 In the Introductions to the 'Cambridge Observations' for 1833-4-5, 

 and the Introduction to the ' Greenwich Observations ' for 1836, will 

 be found several instanced of the way of examining the divisions of 

 astronomical circles. See also article CHICLE, and the references there 

 given. 



( ; I! AFTING is an operation by which a portion of one individual of 

 the vegetable kingdom is applied to another which is within certain 

 limit* of physiological affinity, so as to form a vital union, and con- 

 sequently produce a reciprocal growth. Thus a species bearing small 

 and austere fruit may be cut down, and the remaining part grafted 

 with a scion from a tree of which the fruit is large and delicious ; and 

 being nourished, but not changed in any essential character, this scion 

 will form a tree, ultimately producing fruit similar in every respect, 

 all other circumstances being the same, to that of the tree from which 

 it was taken. The shoots of any particular variety may be cut into 

 many hundred pieces, if sufficiently numerous, and, by grafting, each 

 of them can be made to possess all the properties of an individual 

 tri'e in the course of one season. In the case of cultivated fruits, as 

 well as in many varieties of ornamental plants, multiplication by seeds 

 ui precarious ; and with regard to hybridi it is impracticable, at least 

 no assurance can be had of a reproduction of the same variety ; on the 

 contrary, a disposition is generally manifested to return to the natural 

 wild state of the species. Grafting is in some instances the only 

 means, and in many it is the most eligible, of preventing this. By it 

 the peculiar richness of the fruit or the delicate tint of the flower 

 which we especially prefer and admire can be perpetuated in an almost 

 infinite series of individuals, each being the result of augmentation of 

 the comparatively small original portion this portion being placed in 

 favourable circumstances for receiving an abundant supply of new 

 and proper matter, on which it exercises ite organising powers, and 

 effect** a |erfect assimilation, which causes a similar development of 

 leaves, flowers, and fruit. Again, this newly-formed augmentation 

 being every way similar to that from which it was derived, it will 

 continue to exercise the same functions with regard to such new matter 

 as comes within the extending scope of its organising powers, the 

 progress only becoming arrested by such causes as naturally limit the 

 growth of the parent tree. Propagation by cuttings, it is true, will 

 'y continue the variety unchanged; but that process in numerous 

 instances is slow : in others success is not attainable -to any con- 

 siderable extent. 



From what has been stated, the great importance and utility of the 

 process about to be explained will be sufficiently evident. 



Tbrf limits within which grafting may be effected extend to species 



and varieties of the same genus, or at all events are confined within 



natural order. Pears may be grafted not only on other 



pears, but also on the quince (which is very frequently done), and on 



the medlar, white thorn, or mountain ash. Peaches are budded either 



on the almond, or more frequently on the plum, their own roots not 



being suited to the cold soil of this country. In these cases, although 



ives and fruit of the peach and the plum, the pear and the 



mountain ash, have a very different appearance, yet botanists have 



determined that the stock and the scion belong to the same natural order. 



As one species is pften grafted on another of a different genus, it is 

 necessary therefore to state the reason why such is in many cases more 

 proper than on species of the same genus ; and this leads to the con- 

 sideration of the effects generally produced by the stock upon the graft. 

 When the stock is of slower growth than the graft, as in the case of 

 the white thorn and quince stocks and the pear, the consequence is a 

 partial obstruction of the flow of the sap, which checks the over- 

 luxuriance of the pear-tree, and its natural disposition to produce only 

 wood for a number of years of its youth; the juices, rendered less 

 abundant, become more inspissated, and fruitfulness is induced at an 

 earlier age. This condition may be even carried too far; for the 

 common quince increases so slowly in diameter compared with the 

 generality of pears, that its vessels become inadequate for a sufficient 

 supply of nourishment. The French, aware of this, employ the 

 Portugal quince as a stock for their pears, because its wood increases 

 more in accordance with that of the latter. On the same principle 

 (that is to say, a less copious supply of nourishment) trees are rendered 

 more dwarf than they naturally are, and hence are better adapted for 

 small spaces. On the contrary, a weak species will have a tendency to 

 grow stronger if grafted on one naturally more vigorous. These are 

 modifications induced by the stock on the graft extremely necessary 

 to be known and attended to : for instance, apple-trees on crab-stocks, 

 if injudiciously planted in a small garden, will soon overgrow their 

 limits; whereas on the French paradise stock, the dwarfest of any, 

 they are easily managed within a very small space ; besides, the roots 

 of the latter are very fibrous, and run near the surface, which renders 

 them eligible for planting over a bad subsoil. Many species and varie- 

 ties both of fruits and ornamental plants, natives of a warmer soil, are 

 advantageously grafted on their hardier congeners, such as the peach 

 and apricot on the plum, Chinese tender roses on the wild roses of our 

 hedges, and many ornamental species of Cratogus on the C. Oxya- 

 cantha. 



The methods of grafting are of great variety. M. Thouin (' Mono- 

 graphic des Greffes') has enumerated 43 modes of grafting, 39 of 

 inarching, and 28 of budding. Many of these are however more 

 curious than useful ; and not worth being detailed. It will be better 

 to explain the principle on which all modes of successful practice must 

 depend, either as regards grafting, budding, or inarching. 



It is well known that the bud of a plant has the power of becoming 

 a distinct individual, if separated from the parent and placed in cir- 

 cumstances sufficiently favourable for its future development. But no 

 development can take place unless the portion abstracted from any 

 plant contain either a bud, or the perfectly formed rudiments of one. 

 Hence the portion intended to be propagated must contain a bud or 

 buds. The diametrical increase of exogenous plants proceeds out- 

 wardly, in consequence of the formation of new layers of alburnum, 

 interwoven into the peculiar texture of the tree by extensions of the 

 medullary rays. The alburnum is interposed between the inner Ivuk 

 and the heartwood, with both of which it is in vital or organised union. 

 The greater part of the heartwood of a tree may be bored out, and, 

 though made a hollow cylinder, it will still continue to increase. The 

 outer bark may be removed, and a new one will gradually be formed ; 

 but, if the alburnum be entirely destroyed, death will be the con- 

 sequence. 



It appears therefore that buds with some portion of alburnum are 

 the parts essentially necessary for propagation ; for although the heart- 

 wood and bark be organised, yet they are but passively so, and have 

 not the power of extending organisation to new matter when they 

 are deprived of the media of buds and alburnum. Keeping therefore 

 the importance of the latter in view, the best mode of operation is 

 that whereby the greatest possible extent of the alburnum of the stock 

 and graft is brought into exact contact, without making too extensive 

 a wound. If the sections of alburnum can be made to coincide in 

 every point, the result of the operation will be the most perfect that 

 can be obtained. 



The modes of grafting most generally practised are whip, cleft, 

 saddle, and crown grafting. Of these irhip-graftitig is by far the com- 

 monest, and is performed as follows : the stock is cut over, sloping, 

 above a smooth and straight part. The end of the scion is cut sloping 

 and thin towards the lower end. Then on the same side of the stock 

 as that of the lowest part of the slope made in cutting off its top, a 

 slice is cut clean off, hi length equal to that of the cut part of the 

 scion, and in breadth so as to expose as much of the wood of the stock 

 as will equal that seen in the slanting section of the scion. Both 

 suctions should be smooth and plain, and as regards the alburnum, 

 they should be the exact counterparts of each other ; or, if this cannot 

 generally be the case, the coincidence should be as exact as can be on 

 one side at least. A thin wedge-shaped tongue is made very near the 

 upper part of the slope in the scion, and a corresponding nick in the 

 stock to receive it. The top part of the scion is shortened to two or 

 at most three buds, and fitted to the stock, to which it is tied with a 

 strip of pliable matting ; and the parts so united are then covered 

 with grafting-clay, or some other composition, which remains till the 

 graft has pushed, or as long as there is no danger of the matting, used 

 as a ligature, cutting or galling the parts when they begin to grow and 

 to have an enlarged circumference. After the first loosening it is often 

 advisable to apply slightly a fresh bandage immediately ; and in some 

 cases a little clay or composition may be put round, should the 



