20 ''Reversion'' and Resistance to ''Big Bud'' 



some factor causing a local drought to the young fruits. The presence 

 of an unusual number of growing points may supply the answer. They 

 may absorb the sap that should go to the developing fruits and thus 

 cause a local drought. It may be contended that normal bushes often 

 show a considerable amount of branching and yet bear fruit but this 

 case is entirely different. Here the branching is caused by excess of sap 

 from the roots forcing out buds otherwise quiescent, while in truly 

 reverted bushes the sap is diverted from the single terminal growing 

 point into a number of laterals that would in the ordinary course of 

 events have remained quiescent. In the first case there is enough sap for 

 the fruit buds and more to spare for lateral wood growth and in the 

 second a limited supply diverted from tlie fruits to an unusual number 

 of new growing points. In addition, these extra lateral growths are 

 usually formed comparatively low down on the year's growth and it is 

 possible that as a result they secure the first call on the sap supply. The 

 case may be compared with that of the peach whose method of fruiting is 

 similar. Here also the flowers are borne along the preceding year's shoot 

 and it is a text-book rule to leave a growing point beyond the developing 

 fruits. Failure to do so is said to prevent the fruits from attaining their 

 normal size and in practice often, though not always, does so. In garden- 

 ing language there is nothing to " draw the sap " to the fruit, in conse- 

 quence of which the fruits suffer from a local drought. It cannot be too 

 strongly urged that the whole process of reversion is gradual and at no 

 point can hard and fast lines be drawn. This is not surprising when it is 

 considered what complex factors affect the sap supply to the fruits. It 

 will be dependent on the variety, the climate, the condition of the rooting 

 system, the number of active growing points, and so on. One of the most 

 puzzling points about running of? is the fact that the sap supply to the 

 fruits would appear to be small at the same time when, to judge from the 

 active growth made by the bush, the sap supply elsewhere is large. 

 Apart from the argument outlined above that the abnormal number of 

 sap drawers deprive the developing fruit of sap there is another point to 

 consider. At the time when the outgrowth of laterals begins the growth 

 push is vigorous (see graphs, p. 15). At the time when the fruit drops, 

 which is somewhat later, the general growth push has slackened though 

 the lateral growths are still actively transpiring and making vigorous calls 

 on the sap supply. Strictly speaking therefore the sap supply to the 

 fruits is small at a time when the sap supply has been large to the laterals. 



