124 • Age and Flowering 



With many fruit trees, grafting young scions onto dwarfing 

 stocks is another method whereby both a promotion of flowering 

 and an inhibition of growth are obtained. The stocks are usually 

 varieties of the same or a closely related species, and may be used 

 either as rootstocks or interstocks. The latter method involves first 

 grafting the dwarfing stock onto a standard seedling rootstock and 

 later grafting the variety to be dwarfed onto the developed dwarfing 

 tissue, so that the latter is interposed between root and crown. 

 The mechanism by which such procedures cause early flowering 

 is not known, but may in some cases be related to the reduction 

 of phloem transport out of the scions and thus analogous to 

 girdling. However, the interactions between stock and scion in such 

 grafts are often highly specific, and not all grafts that reduce growth 

 or transport promote flowering. In addition, not all grafts that 

 cause early flowering and dwarfing appear to involve inhibited 

 phloem transport (Sax, 1958b). 



Another traditional method of handling fruit trees, the espalier 

 technique, in which branches are bent horizontally or downward 

 out of their normal direction, suggests that orientation with respect 

 to gravity may affect flower initiation. This supposition was directly 

 tested with young plants of several kinds of fruit trees by Wareing 

 and Nasr (1958), who found marked effects on apples. Nineteen 

 young shoots held in a horizontal position initiated a total of 116 

 flower buds in contrast to a control series initiating 5. Smaller but 

 similar effects were observed in cherries (Primus). Similar results 

 have also been obtained by Longman and Wareing (1958) on young 

 Japanese larch (Larix) trees. These are all, of course, reminiscent 

 of results with pineapple and soybeans that may involve a changed 

 auxin distribution, and it has also been suggested that the flower- 

 promoting effects of bark inversion may be due to effects on auxin 

 distribution, which then affect phloem transport (Sax, 1958b). 



As repeatedly noted, most of the methods described above 

 have in common either a demonstrated or possible effect of causing 

 the accumulation of photosynthate near the growing points affected. 

 The promotion of flower initiation in some trees by the early 

 removal of fruits might also be attributed to an increase in avail- 

 able carbohydrates (for experiments of this kind dealing with Citrus, 

 see Furr and Armstrong, 1956). The general hypothesis that ma- 

 turity, and hence flowering, in many trees depends on a high level 



