sept, ii PHYSIOLOGY 229 



In spite of the apparent physiological union between the old stock and the 

 newly-formed growth, from a morphological standpoint they lead an altogether 

 separate and distinct existence. In its structural character, forms of tissues, 

 mode of secondary growth, formation of bark, etc., each maintains its own individu- 

 ality. In special cases it has been affirmed that they do mutually exert, morpho- 

 logically, a modifying effect upon each other (Graft-hybrids). In practice several 

 different methods of inserting cuttings are in use, but only the more important 

 can be mentioned here. 



Grafting is the union of a shoot with a young and approximately equally- 

 developed wild stock. Both are cut obliquely with a clean surface, placed 

 together, and the junction protected from the entrance of water and fungi by 

 means of grafting wax. 



Cleft or tongue grafting is the insertion of weaker shoots in a strongei 

 stock. Several shoots are usually placed in the cut stem of the stock, care being 

 taken that the cambial region of the different portions are in contact, that the 

 cortex of the shoots is in contact with that of the stock. In other methods of 

 grafting the cut end of the shoot is split longitudinally and the cut shoot 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 the space cut 

 between the bark and the splint wood (Fig. 193, I). 



In lateral grafting, the shoot, after being cut down, is wedged into a lateral 

 incision in the stock. 



A special kind of grafting is known as budding (Fig. 193, III). 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 -shaped piece of bark, which is easily 

 separated from the wood when the plants contain sap. 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 piece 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. 

 Budding is especially used for roses and fruit-trees. 



The Phase of Elongation 



For the performance of their proper functions, the embryonic 

 rudiments of the organs must complete their external development. 

 They must unfold and enlarge. 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 water — that is, by the 

 incorporation of an inorganic substance which is most abundantly 

 supplied to them from without, and to obtain which no internal 

 nutritive processes are first necessary. The elongation of a plant 

 organ to its definite extension, whereby it is often enlarged a hundred 

 or thousand fold, may be compared with the extension of certain animal 

 organs by means of an influx of water, as occurs in the case of the 



