2i8 BOTANY OF THE LIVING PLANT 



truit 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, it has been stated that occasionally 

 a more intimate fusion of charactei-s of the stock and of the scion has been 

 set up. Reputed graft-hybrids exist. The most notable is Cytisus adami, 

 of which the parental forms are stated to have been the common yellow 

 Laburnum and Cytisus purpiireus, 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. It was suggested that nuclear fusion, of a sexual nature, took 

 place in the region of the callus of the graft, and was the source of the fusion 

 of the characters. A recent careful examination of its nuclear details makes 

 this explanation appear improbable. There is even historical reason as well 

 as comparative probability for an alternative suggestion, which has met with 

 acceptance. It is held that the plant from which the original purple graft 

 was taken was itself not a pure species, but a hybrid ; in which case the facts 

 would follow as recorded. Thus the probability is that Cytisus adami is not 

 a graft-hybrid. Better evidence will be necessary before the existence of 

 graft-hybrids can be held as proved. 



The hovticulturalist also induces the formation of adventitious buds, 

 and some plants respond freely. If a lamina of Begonia or of Gloxinia 

 be cut transversely across the main ribs, and be cultivated in heat on 

 damp soil, buds may be formed in relation to any cut vein. These buds 

 root themselves in the soil as new plants. It is stated that each 

 bud arises from a single cell of the parent leaf. (Fig. 167.) Certain 

 Fern-rhizomes, and even the bases of their leaves behave in a similar 

 way ; but it is in the Mosses that there is the most remarkable pro- 

 fusion of this adventitious development from single cells of the injured 

 part. If moss plants be chopped up into small pieces, any piece in 

 which an uninjured cell remains may start a new vegetative growth, 

 and lead ultimately to a new moss plant. 



There are certain weeds of farm land which depend upon a some- 

 what similar vegetative multiplication for their survival, when the 

 land is worked by plough and harrow. The Couch Grass [Triticum 



