102 REPRODUCTION OF PLANTS. 



All parts of plants have the power of uniting 

 together by their cellular tissue, thus we see 

 even in those which consist only of cellular sub- 

 stance, that such adhesions take place. The name 

 of graft has been especially given to one case of 

 adhesion, that in which the liber, and particu- 

 larly pith, of two plants unite so nicely together 

 that the part called the graft can receive its sap, 

 and thus live by the nourishment it derives 

 through the organs of the old plant ; thus arti- 

 ficially doing what parasitic plants, such as the 

 mistletoe, do by nature. There is, however, a 

 limit to this operation ; if we except parasitical 

 and some few natural adhesions, we shall find 

 that artificially it is only plants of the same na- 

 tural family that can be grafted together with 

 any thing like permanent success, and only those 

 of families strongly analogous in which any 

 union will take place at all. When they are 

 not of the same family the grafts are of short 

 duration in consequence of their physiological 

 difference from the tree to which they have been 

 united. Grafts are of three kinds that ordi- 

 narily so called, in which a severed portion of a 

 stem is united to another tree, whose bark has 

 been cut away at the proper spot, that by ap- 

 proach, which consists of drawing two branches 



