DIV. ii PHYSIOLOGY 297 



or when an organ is experimentally brought into a position it did not 

 previously occupy. 



The first result of the removal of an organ may be the appearance 

 of so-called COMPENSATIONS ; other remaining organs become larger. 

 The leaves which arise at the growing point prevent older leaves 

 attaining their maximal size, and if the growing point is removed the 

 size of the leaf may be increased (e.g. in the tobacco plant). The 

 active development of some of the axillary buds hinders that of many 

 others ; if the dominant shoot is removed the resting buds commence 

 to grow. The conclusion may be drawn that even in normal develop- 

 ment the size of the organs is determined by correlative influences 

 from neighbouring organs. In other cases a QUALITATIVE effect 

 follows the removal of an organ. If the tip of a Pine is removed, its 

 place is taken by one of the adjacent lateral branches, which assumes 

 the erect position and shows the same leaf arrangement as the original 

 main shoot. It appears that the usual oblique position and dorsi- 

 ventral arrangement of the foliage on the lateral branches comes 

 about under the influence of the main shoot. In this and many other 

 cases of correlative influence it is not necessary that the organ should 

 be removed ; as a rule it is sufficient to interfere with its normal 

 action, as for example by embedding it in plaster of Paris. 



It has been shown in treating of restitution (p. 282) that new 

 roots or shoots may be produced on isolated organs. Thus the 

 members of the plant, like every cell, are originally capable of further 

 development in a number of directions. It is their mutual influence 

 that serves to control this. 



The effect of correlation is also shown when an organ is trans- 

 planted to a new position. By methods of transplantation, which 

 have been derived from horticultural practice, it is easy in the case of 

 many plants to make a separated part grow in relation to a wounded 

 surface. The separated part is termed a graft, while the plant upon 

 which it is inserted is called the stock. The graft may be of the same 

 species as the stock, or from a related kind of plant. One correlative 

 influence which is apparent is the suppression of regeneration on the 

 part both of the stock and the graft. The latter adopts the root- 

 system of the stock, while the stock in turn adopts the shoot-system 

 of the graft ; there is no necessity for the formation of new organs. 



Artificial GRAFTING, like artificial propagation, plays an important part in 

 horticulture. Separated shoots bearing buds serve as the grafts or scions, and are 

 caused to unite with a rooted plant as the stock. In this way it is possible to 

 obtain examples of considerable size of a race or species more rapidly than by 

 seeds or by artificial propagation. In practice several different methods of insert- 

 ing grafts 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 (Fig. 263 II}. Cleft or tongue grafting is the insertion of 



