1(3 ''Reversion'' and Resistance to '' Bhj BufV 



strengthened during the previous season and it is they that now grow out 

 into twigs of various lengths. 



There is also often some growth made from one or both of the 

 accessory growing points present in the highest fruit laterals. It is 

 usually only slight and may be explained by the fact that though these 

 growing points are weak the growth push of a fruit tree is always at its 

 maximum at the top of the yearly growth. The previous year, when they 

 failed to grow out, their growing points were still weaker and the growth 

 push of the plant as a whole was decreasing, but in the spring of the 

 current year not only are they stronger but the growth push of the plant 

 is increasing to a maximum. 



Weak shoots show a slightly different behaviour from that just 

 described for a strong shoot. A weak shoot usually means that terminal 

 growth ceases early in the season and that therefore when mites are 

 fairly abundant nearly all the laterals become " big." Such shoots do not 

 form wood buds at the base and therefore no growing out takes place 

 from that region. Generally there is a small amount of outgrowth from 

 any lateral bud that has escaped mite but often the shoot becomes 

 entirely bare and all growth from it ceases. 



Where mites are very abundant and the bush is still making strong 

 growth a slight variation occurs from what has been described. Here the 

 check to the terminal bud in the first year is so strong that it disappears 

 altogether during the summer while growth is still active and the laterals 

 immediately below are thus stimulated to strong outgrowth the same 

 year. This case must be distinguished from the previous one where the 

 terminal, though checked, continues growing during the current season 

 and only fails to grow next season because it has become a big bud. As 

 explained below in the section treating the growth graphs of the black 

 currant removal of the terminal in the winter causes buds far below it 

 to shoot while removal in the summer causes buds just below it to shoot. 



Case 2. Reversion of a Big Bud resistant variety. 



At first sight it would seem that if Big Bud were a necessary ante- 

 cedent to Reversion, resistant varieties should be free from it. Through 

 the kindness of Messrs Seabrooks of Chelmsford I have been enabled to 

 study some very interesting cases of reversion on the variety known as 

 "Seabrook's IMack." As the term "resistant" implies the variety docs 

 not under ordinary circumstances become badly attacked. In the firm's 

 experience some big buds are sometimes formed but they never increase 

 seriously in numbers and the bushes as a whole remain practically free. 



Reverted wood of this variety differed from Long Ashton material in 



