DAMEl's EXl'liRlMIiiXTS AND LUMLL'SIUXS 163 



Accumulation of reserve material in vejietative plant parts has no 

 special importance in grafting, as proved by grafting turnip and 

 cabbage, kale and kohl rabi, Brussels sprouts and kohl rabi, and 

 kohl rabi and caulitlower. [These plants, though very different in 

 form as cultivated, are all, except turnip, varieties of one species, 

 Brassica oleracea — M. G. K]. Even grafting by approach 

 between roots of lettuce and aged salisfy succeeded, though 

 the inulin of the salsify did not circulate in the lettuce cells. If the 

 cell contents of one of the plants approached are toxic for the 

 other, the graft fails. 



If a large and a small variety are grafted on each other the 

 larger will develop to the detriment of the smaller, which will re- 

 main nearly dwarf. Plants of different forms, like kale and cauli- 

 flower [see bracket note above], may make good unions. Plants 

 in active growth may be grafted by approach on plants at rest; 

 e. g., seedling cabbage several weeks old was grafted in spring with 

 perfect success on a turnip whose root was fully formed. Grafting 

 by approach succeeds between annuals, biennials, and perennials; 

 also between biennials and perennials. The fact that hr and linden, 

 and Araha SpDWsa and A. Sicboldii were grafted by approach 

 shows deciduous and evergreen plants may be intergrafted. 



213. Extrinsic conditions. — With grafts proper all extrinsic con- 

 ditions are present, but in cutting off the top of the stock and sup- 

 pressing the absorbing apparatus of the cion, there is danger of 

 the death of both plants. Another fundamental extrinsic condition 

 of success must be maintenance of life in the two plants till siic-, 

 cess is complete.. The cion is sometimes preserved by being 

 placed in water as soon as made to prevent its drying out, keep 

 the surface clean, and prevent the formation of sugar or other ma- 

 terial on the cut surfaces. This might interfere with the free pas- 

 sage of sap from stock to cion. 



In order that the cion may grow its turgescence must be re- 

 established- This is secured by the imbibition of the crude sap of 

 the stock by the cells of the cion, and occurs more quickly ac- 

 cording as the crude sap is presented in considerable quantity, 

 but also more cjuickly if the initial turgescence of the tissues of 

 the cion has not been diminished during the preparation of the 

 graft and its being put in place. This explains why it is necessary, 

 to operate quickly and why cuttings are often made under water 

 where the cion preserves much of its turgescence and produces 

 good results. It also accounts for the good eft'ects of wax-like 

 material used in open air grafting; the utility of the collar graft, 

 because the osmotic force is strongest at this level : and the im- 

 portance of the time of day in operating, because the osmotic force 

 varies, being strongest in the evening (hence the greater success 

 then). The re-establishment of turgescence in the graft is con- 

 sidered fundamental to success, therefore it is impossible to graft 

 parts incapable of retaining turgescence or which do not possess it. 



214. Intrinsic conditions. — In the graft proper plants incapable 

 of regenerating their tissues cannot be grafted. In gladiolus and 



