420 TEXTBOOK OF BOTANY 



from stock cells, or from both kinds of cells. If the primordium of the 

 pistil develops from both kinds of cells, some of the tissues in the 

 resultant fruit will resemble those in the fruit of the scion, and others 

 will resemble tissues in the fruit of the stock. 



When the tissues characteristic of one kind of plant surround those 

 of the other, the chimera is said to be periclinal; when neither tissue sur- 

 rounds that of the other, but each appears in distinct sectors, the chimera 

 is sectorial. Incomplete periclinal chimeras appear superficially to be 

 sectorial. 



Experimental attempts to increase the number of chimeras include 

 wounding or cutting across the stem at the junction of stock and scion 

 after they have become united. 



Advantages of grafting. Grafting is a valuable means of perpetuating 

 desired varieties of plants that do not multiply readily by other methods 

 of vegetative propagation or reproduce true from seeds. There are also 

 certain other advantages, three of which will be mentioned briefly. 



The range of distribution of a variety may be extended if it can be 

 grafted on root svstems that grow better than its own roots in certain 

 habitats. For example, peach trees may grow better on the roots of plum 

 in poorly drained soils, and plum trees may grow better on roots of peach 

 in light or sandy soils. The root systems of some varieties of pear grow 

 well in light, well-drained soils, others in heavy, poorly drained soils. 



The destructive effects of insects, fungi, and bacteria on roots may be 

 avoided by grafting the desired variety on root systems that are immune 

 to these parasites. A classical example is the avoidance of the destruc- 

 tive effects of the root louse. Phylloxera, on roots of the wine grape, Vitis 

 vinifera, of France by grafting the European grape on an immune species 

 of American grape, Vitis lahnisca. Similarly, certain susceptible varieties 

 of apple are grafted on the roots of other varieties immune to the woolly 

 aphis. English walnut is protected from the fungus Armillaria by being 

 grafted on black walnut, which is immune to it. 



Plants, such as apple, have a long vegetative period before they bear 

 flowers and fruits. The shoots of apple seedlings will bear fruit in two 

 or three years if they are grafted on the branches of a tree that has 

 begun to bear flowers and fruits. Advantage is sometimes taken of this 

 fact in testing the quality of apple seedlings that would otherwise not 

 bear fruit for ten years. 



Root cuttings. Root cuttings are made from several kinds of plants, 

 such as blackberry, red raspberry, plum, cherry, horse-radish, apple, 

 Japanese quince, sumac, phlox, and anemone. The cuttings, which are 



