364 TEXTBOOK OF PLANT PHYSIOLOGY 



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. It is easy to graft different varie- 

 ties 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 

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

 the investigations by Vochting and Winkler. 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 pre- 

 serving 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 artichoke (Helianthus tuberosus) 

 it is in the form of inulin. If a sunflower is grafted upon the arti- 

 choke, tubers of the usual type are formed on the roots of the latter 

 and these are filled with inulin, though the material for its forma- 

 tion is supplied by the sunflower. Sometimes, however, specific 

 qualities are transmitted from one part of the graft to the other. 

 Thus, for instance, 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. Thus, in grafting an apple tree upon the Para- 

 dise stock or a pear upon the quince, the time 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. Vochting's 

 experiments with beets are of exceptional interest in this connec- 

 tion. He grafted the adventitious buds, developing at the base of 

 the inflorescence, into one- and two-year-old roots. In the first 

 case they produced vegetative shoots, in the latter, flower-bearing 

 shoots. If blossoming is induced by specific hormones, then this 

 experiment must be interpreted as a diffusion of these hormones 

 from the stock into the scion. 



