SECT. II PHYSIOLOGY 255 



the shoots is in contact with that of the stock. In other methods of grafting, tlie 

 cut end of tlie shoot is split longitudinally and the cut shoot is inserted in the 

 periphery, or a graft may be inserted in the cortex or in the side of the stock. In 

 grafting in the cortex the flatly-cut shoot is inserted in tlie space cut between the 

 bark and the splint wood (Fig. 208, /). In lateral grafting, the shoot, after being 

 cut down, is wedged into a lateral incusion in the stock. 



A special kind of grafting is known as buddixg (Fig. 208, ///). In this process 

 a bud ( " eye ") and not a twig is inserted under the bark of the stock. The " eye " 

 is left attached to a shield-shaiied jiiece of bark, which is easily separated from 

 the wood when the plants contain sajj. The bark of the stock is opened, by a 

 T-shaped cut, the " eye " inserted, and the whole tightly covered. Occasionally 

 some of the wood may be detached with the shield-shaped j'iece of bark (budding 

 with a woody shield). In the case of sprouting buds, the budding is made in 

 spring ; in dormant buds, which will sprout next year, in summer. 



The union is accomplished by means of a callus (p. 162), formed by both 

 the scion and the stock. Vessels and sieve -tubes afterwards develop in 

 the callus, and so join together the similar elements of both parts. Such 

 an organic union is only possible between very nearly related plants : thus, for 

 example, of the Amygdalaceae, the Plum, Peach, Almond, and Apricot may 

 readily be grafted one upon the other ; or of the Pomaceae, the Apple with the 

 Quince ; but not the Apple with the Plum, nor (as has been asserted) with the Oak. 



In spite of the physiological union between the old stock and the newly - 

 formed growth, from a morphological standpoint they lead altogether separate 

 and distinct existences. They may, however, exert an influence on each other ; 

 thus annual plants grafted on biennial or perennial stocks attain an extended 

 period of existence. In structural character, forms of tissues, mode of second- 

 ary growth, formation of bark, etc., each maintains its own individuality. In 

 special cases it has been affirmed that they do mutually exert, morphologically, a 

 modifying effect upon each other (graft-hybrids). (Fig. 221) (*'^). 



II. The Phase of Elong-ation 



For the performance of their proper functions, the embryonic 

 rudiments of the organs must unfold and enlarge and assume their 

 characteristic appearance. This subsequent enlargement of the 

 embryonic organs of plants is accomplished in a peculiar and 

 economical manner. While the organs of animals increase in size 

 only by a corresponding increase of organic constructive material and 

 by the formation of new cells rich in protoplasm, and thus require 

 for their growth large supplies of food substance, plants attain the 

 chief part of their enlargement by the absorption of Mater — that is, 

 by the incorporation of an inorganic substance which is most abund- 

 antly supplied to them from Avithout, and to obtain which no 

 internal nutritive processes are first necessary. 



The absorption of water by living cells does not take place with the same 

 rapidity and Mithout interruption as in the case of porous bodies. Before the cells 

 can take up additional water they must enlarge by actual processes of growth. 

 The water, penetrating the young cells by imbibition or by the force of osmotic 

 pressure, is uniformly distributed through the protoplasm, which fills the cell ; 



