INTERRELATIONS BETWEEN PARTS OF PLANTS 405 



phloem elements is of especial importance. As has been seen, it 

 is these elements that are the centers where the (Villus formation 

 begins and where it is most vigorous. Very often a thickening 

 of the stem, which is caused by an excessive development of 

 the callus, is formed at the place of junction of the stock and 

 scion. The joining of the two parts will be the easier, the nearer 

 they are related to each other. One can graft different varieties 

 of the same species, but it is also possible to unite two species 

 of the same genus and even of different genera of the same 

 family. 



Various methods of grafting and budding have been used in 

 horticultural practice since very ancient times. But only 

 recently has the subject been put to a scientific analysis, chiefly 

 through the investigations of Vochting (1892), Winkler (1912), 

 and Krenke (1928). The most important question seems to be 

 the reciprocal effect of the stock and the scion, the two together 

 representing a united organism. The roots of the stock supply 

 the leaves of the scion with mineral nutrients, while the leaves, 

 in their turn, send to the roots organic compounds. Still, 

 despite this very close relationship, the two parts of a grafted 

 plant are independent of each other, each preserving its own 

 peculiarities as well as its specific storage products. Thus, for 

 instance, in the sunflower, carbohydrates are stored in the form 

 of starch ; while in the Jerusalem artichoke (Helianthus tuberosus) , 

 the storage form is inulin. Now if a sunflower is grafted upon 

 the artichoke, tubers of the usual type are formed on the roots 

 of the latter, and these are filled with inulin, though the material 

 for its production is supplied by the sunflower. Sometunes, 

 however, specific qualities are transmitted from one part of the 

 graft to the other. For example, in grafting tobacco upon the 

 potato, the specific alkaloids of the tobacco are transported to 

 the potato stock. 



Still, in grafting, a quantitative effect is more common than is 

 a qualitative one. In grafting an apple tree upon the paradise 

 stock or a pear upon the quince, the tune of fruiting is hastened, 

 which often is of great advantage. The duration of life, however^ 

 is shortened. An apple tree upon paradise stock dies at the age 

 of 20 to 25 years, while normally it may live for 200 years. While 

 a reciprocal effect of the stock and the scion undoubtedly exists, 

 it must be, generally, insignificant. A score or two of choice 



