VEGETATIVE PROPAGATION 251 



The bud or graft retains its original qualities. But according to the 

 vigour of the stock it may mature earlier in the season, and fruit more 

 profusely than upon its own root. Besides such advantages, time is 

 also saved. For it is much quicker to insert a graft or bud upon an 

 established stock than to raise an equally strong plant from a cutting. 



The graft, or bud, or scion, as it is often called, need not necessarily be of 

 the same species as the stock upon which it is placed. For instance, the 

 Peach may be grafted on a Plum stock, the Apple on the Pear, the Pear on the 

 Quince, or the Medlar on the Hawthorn. But the affinity must be close, such 

 as within the Natural Order. The stock often influences the scion, though 

 the latter retains its essential characters. The size, age of coming into fruit, 

 or the period of maturing of the fruit may be affected ; but such changes are 

 ascribed rather to the nutritional capacity of the stock than to any more 

 profound cause. On the other hand, a more intimate association of the 

 characters of the stock and of the scion is occasionally set up. Reputed 

 Graft-Hybrids exist, which appear to share the characters of stock and scion. 

 The most notable of these is Cytisus Adami, of which the parental forms are 

 stated to have been the common yellow Laburnum and Cytisus purpureas, 

 the latter having been inserted on the former. The plant which resulted has 

 been widely propagated. It shows usually purple flowers, but certain branches 

 " throw-back " to the common yellow form. 



Others have also been raised artificially ; the most notable of these were 

 from grafts between Solarium nigrum, the black Nightshade, and S. Lyco- 

 persicum, the Tomato. A wedge or saddle-graft is made, and after the tissues 

 have united the graft is cut through transversely : this causes a callus 

 to be formed with numerous buds. Most of these show only the characters 

 of the stock, or of the scion : but some show those characters intermingled. 

 For instance, the shoot might be almost equally divided so that one side of it 

 is Nightshade the other Tomato. Such monstrous forms are called " chim- 

 aeras," and the above instance would be distinguished as a sectorial chimaera, 

 owing its origin to a lateral coalescence of the tissues of scion and stock, 

 without any actual fusion of the cells. Others are called periclinal chimaeras, 

 where the superficial cells of the apex arise from one source, the inner cells from 

 the other, but again without cell-fusion. It appears from detailed examination 

 of its tissues that Cytisus adami is a chimaera of the latter type. Chimaeras are 

 not hybrids in the true sense of the word. There is no nuclear fusion, but the 

 buds arise from a mechanical coalescence of tissues from the two parents at 

 the junction of stock and graft. Each retains its own individual qualities, 

 however closely the two may appear to be physiologically related together. 



But occasionally a true graft-hybrid may occur, produced by fusion of cells 

 and of their nuclei. An example is seen in Solatium darwinianum raised by 

 Winkler, which is found to be intermediate between Nightshade and Tomato 

 even in the number of its chromosomes. The nuclei of the former show on 

 division 72 chromosomes, but those of the latter have only 24. The germ- 



cells of 5. darwinianum are found to have 48, that is — — — . It may there- 

 fore be concluded that a fusion of a nucleus of Nightshade (72) has actually 



