22 " Eeversion'' and Resistance to '' B'uj Bud'' 



Transfer them however to a wet climate like Long Ashton and they con- 

 tinue to increase regularly and the variety apparently loses its resistance. 

 If this theory is sound there should also be some explanation why Boskoop 

 is not resistant at Chelmsford, since in that climate it has a more definite 

 summer check than at Long Ashton. This is partly, at any rate, supplied 

 by the fact that, as already pointed out, the summer check has much 

 more effect on Seabrook's than on Boskoop. This habit of an early check 

 to growth may be sufficient in itself to explain the mite-resistance but 

 on the other hand there may be other factors which influence the result. 

 There is however nothing in the evidence so far in the author's possession 

 which would lead to any other conclusion. It would thus appear 

 possible, by arranging the cultural conditions in such a manner as to get 

 a marked and continued summer check, to cause " Big Bud " to disappear 

 almost entirely from an infected plantation. Such a treatment will be 

 tried in the near future. 



The graphs of Table I serve to explain the character of the reverted 

 wood in a typical shoot of Seabrook's Black. The terminal bud is either 

 blind or a killed bud which means that it was attacked comparatively 

 late in the season. The following year there is no strong terminal growing 

 point to take the growth push so that this is distributed amongst the 

 accessory growing points in the flower buds according to their strength 

 and also according to their nearness to the apex of the shoot. The lowest 

 buds (0 to 50) are not only weak but far from the apex and therefore are 

 unmoved. The next two are stronger but being still fairly far from the 

 apex usually make but a short growth. The next six are comparatively 

 strong and usually make a considerable growth while the last five or six 

 are so weak that, despite the extra push due to their nearness to the 

 apex, they make but a short growth. Fig. 11 shows the kind of growth 

 obtained in reverted shoots grown under Chelmsford conditions and 

 agrees fairly well with the theoretical expectations. 



Case 3. A. No Big Bud present. Killed buds extremely few or absent. 



In addition to the material already described were shoots from Messrs 

 Seabrook's from reverted bushes not showing any big buds. The 

 terminals here were apparently normal and there were very few killed 

 lateral buds. The fact that killed buds were to be found suggested the 

 possibility that the original terminal had been killed and its place taken 

 by one of the accessory growing points originally present in the terminal 

 bud. This does sometimes undoubtedly happen, as may be seen in 

 Fig. 10 which shows the killed terminal in a Seabrook's Black twig. The 

 small bud immodiatoh' latornl to the blank terminal is one of the 



