59 



in the normal leaf there are five main, veins, A, i5, C, JD, & r 

 and these run from the top of the leaf stalk, to a point at the 

 margin.* From the middle main vein, or midrib C, a series of 

 sub-main veins run to points on the margin and it is the 

 number of these sub-main veins which provides one indication 

 of the degree of " Reversion." If less than five are present 

 the leaf is " reverted," if five or more the leaf is probably 

 n6nii;\l. For. further details the reader is referred to the paper 

 quoted. 



The second indication is- afforded by the leaf margin. If 

 finely-toothed with 4 to 8 teeth between C and X not receiving 

 a sub- main vein, the leaf is almost certainly normal, but if 

 coarsely-toothed, with less than four fine teeth not receiving 

 sub-main veins, the leaf is to some degree " reverted." (Ihe 

 maximum number of unveined teeth on a healthy leaf probably 

 varies with the variety.) In leaf No. 4, which shows a medium 

 stage of ' ' Reversion ' ' and one which is of common occurrence, 

 the sub-main veins are reduced to three and many of the teeth 

 have disappeared. In No. 5 there is a further reduction and 

 in No. 7 the extreme or " Oak-leaved " type is reached. 



Identification by shape and size is less certain. " Reverted " 

 leaves are usually small and often long and narrow, but not 

 ahvuys. so. If, for instance, a " reverted " bush grown urfder 

 good cultural conditions be cut to the ground, the following 

 season's growth has quite large leaves which at first sight, 

 appear to be also almost normal in shape, but their " re- 

 verted " character is quickly revealed by the method outlined 

 above. Conversely, small leaves are not necessarily " re- 

 verted," such leaves, quite normal in character, being produced ; 

 frequently, both at the beginning and at the end of the growing; 

 period. 



Date at which Inspection should be made. It is important 

 to note the season during which ' * Reversion ' ' may be best 

 detected. A diseased bush may start growth by producing- 

 normal leaves; but soon after (about the middle of May at 

 Long Ashton) the ' ' reverted ' ' leaves begin to appear and 

 they continue to develop to the end of June. Additional leaves 

 of this type may develop later, but very often the foliage 

 produced in July and August is very much less " reverted ' 

 and, by overtopping the badly affected leaves, is more con- 

 spicuous. No attempt to identify the disease should be made 

 early in the season. May and June are the best months and 

 if it is desired to do the work after this period, the shoots 

 should be turned back and the May and June leaves examined. 



It should be noted finally that the whole bush does not 

 necessarily become affected at the same time. The bushes may 

 " revert " by degrees, branch by branch becoming affected. 



* For the sake of convenience only half of the leaf is shown in theee 

 illustrations, but the amount of reduction is the same on both halves 

 of the leaf. 



