GROWTH OF THE STEM. 



33 



downwards and covered with earth ; and some- 

 times it is made upon tlie upper brandies, which 

 are made to pass through a vessel filled with 

 peat-earth. To facilitate this process, an incision 

 is generally made at the base of the young 

 branch, or a tiglit ligature is applied to it, in 

 order to favour the formation of roots. These 

 roots are buds which, on being immersed in 

 earth, become elongated into slender radicular 

 fibres ; whereas, if left in the air, they would be 

 developed into young scions. This mode of pro- 

 pagation is employed for many plants, such as 

 Pinks, Hortensise, Heaths, Gooseberi-ies, &c. 



2cZ/y, Propagating by slips differs from the 

 preceding method in this respect, that the young 

 branch is separated from the stock previously to 

 its being fixed in the ground. There are trees 

 of which slips take root very readily. In gen- 

 eral, those of which the wood is white and light 

 succeed best. Thus a slip of willow, poplar, or 

 lime, on being stuck in the ground, takes root 

 there in a short time, and soon shoots up vigor- 

 ously. A slip succeeds with more certainty 

 when two or three young buds are left under 

 ground; that is, upon the lower part of it. 

 These buds become elongated into roots, which 

 singularlj' aid the suction by which the develop- 

 ment of the young scions is to be effected. Not 

 unfrequently incisions are made at the base of 

 the slips, or ligatures applied, to facilitate the 

 gi'owth of the roots. Sometimes they are even 

 split longitudinally at their base, and a piece of 

 sponge, soaked in water, is inserted. Some woody 

 species are very difficult to be propagated by 

 slips, such as the pines, oaks, heaths, and in 

 general trees with very dense or resinous wood. 



Hdly, Grafting is an operation by which a bud 

 or young scion is inserted upon an individual, 

 and is there developed so as to become identified 

 with the stock on which it has been placed. 

 Grafting can only succeed when it is performed 

 between vegetating parts. Thus, wood cannot 

 be grafted, nor even alburnum. In the opera- 

 lion and phenomena of gi-afting, the great simi- 

 larity which exists between buds and seeds, es- 

 pecially with respect to tlieir development, may 

 be remarked. These two organs are destined to 

 give rise to new individuals, some of which live 

 at the expense of the stock on which they are 

 developed ; while the rest subsist by themselves, 

 and without requiring foreign assistance. 



It is to be remarked, that grafting, or union 

 of parts, can take place only between vegetables 

 of the same species, species of the same genera, 

 or, lastly, genera of the same family ; but never 

 between individuals belonging to diiferent na- 

 tural orders. For example, the peach may be 

 grafted upon the almond, the apricot on the 

 plum, the pavia on the horse-chestnut ; but the 

 operation would not succeed between the latter 

 tree and the almond, it being necessary that 



tliere should be a kind of agreement or similarity 

 between the sap of the two individuals before 

 the union of a graft can be effected. 



It is the cambium or proper juice of vegeta- 

 bles that serves as a means of union between 

 tlie individual and the graft, in the same manner 

 that in animals coagulable lymph is interposed 

 I)etween the two lips of a recent wound, which 

 it brings together and unites. When the 

 wound of a graft is examined about a fortnight 

 after the operation, a thin layer of small greenish 

 granulations, dispersed in a viscid fluid, is seen 

 between the two parts that have been brought 

 together. These granulations, the rudiments of 

 vegetable organization, are produced by the 

 cambium, which becomes solidified and organ- 

 ized ; and this phenomenon takes place whenever 

 a superficial wound is made upon a tree, pro- 

 vided the contact of air be prevented. 



Several advantages are derived from this 

 method of multiplying vegetables. Thus, it is 

 used for perpetuating remarkable varieties or 

 monstrosities, which could not be reproduced by 

 means of seed ; for procuring quickly many in- 

 teresting trees, which are with difficulty multi- 

 plied by any other means; for hastening the 

 fructification of certain vegetables by several 

 years ; for improving and propagating the varie- 

 ties of fruit-trees, &c. There are four different 

 methods of engrafting. 



1. Grafting hy approach. This process is 

 performed between two plants growing by the 

 roots, and which it is intended to unite by one 

 or more points. For this purpose, wounds ex- 

 actly corresponding to each other are made upon 

 the parts which are to be gi-afted. Plates of 

 bark of equal size are removed, and the wounds 

 thus produced are kept together, and protected 

 from the contact of air, when union takes place 

 between them. By this method, stem, branches, 

 and roots may be united, and fi-uits, or even 

 flowers, may be grafted upon leaves. 



2. Grafting hy scions. Grafting by scions is 

 pei-formed with young twigs, or even with roots, 

 which are separated from the parent plant to be 

 placed upon another, in order to live upon it and 

 be developed at its expense. The twigs which 

 are to be grafted are generally separated some 

 daj's, and in some eases even several months, 

 before the operation is performed, that they 

 may have less sap than the stocks on which they 

 are to be placed. In this case, they are kept 

 alive by immersing their lower extremity in 

 water or in earth. 



Before this kind of grafting is performed, the 

 head of the stock on which it is to be practised 

 is commonly cut off. Sometimes the stock is 

 cut close to the ground, especially in trees in 

 which the graft requires to be placed in the 

 earth, as in the vine, &c. Before this species of 

 grafting can succeed, it is necessary that the 



