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obscure. It does not represent reversion in the strict sense of 

 reverting to a previous type. It is apparently not caused by any 

 fungus, and insects are not directly responsible, though possibly 

 their attacks may not be altogether unconnected with it. In 

 spite of this unsatisfactory state of knowledge, it is felt that 

 the issue of a leaflet on the subject is justified, not only to 

 enlighten those not fully aware of the existence of " Rever- 

 sion," but to point out measures which will help to prevent- 

 further spread of the trouble. The disease has been studied 

 for many years by Mr. A. H. Lees of the Long Ashton 

 Research Station, and much of the information given in this 

 leaflet is based on an article by him which appeared in the 

 Ministry's Journal for March, 1921. It should be clearly 

 understood that the account given below does not profess to be 

 final, and that with continued research further information 

 may be early expected. 



Description of the Disease. General Characters. 

 " Reversion " shows itself in several ways. (1) The most 

 obvious symptom is the change in the character of the leaves, 

 which become elongated and narrow and often assume the 

 " nettlehead " form, as is described more fully below. (2) 

 There is a progressive change, as the trouble develops, in the 

 form of flower- truss and in the flowers themselves. (3) There 

 is ultimately an almost complete failure to produce fruit. It 

 should be clearly understood, however, that " Reversion " is 

 quite distinct from the trouble known as " Running-off" which 

 occurs on perfectly healthy bushes. This is a very widely- 

 spread phenomenon and is often mistaken for " Reversion." 

 In an important paper recently published* it is shown that 

 " running-off " on healthy bushes is due to ineffective pollina- 

 tion. When such bushes are effectively pollinated, either by 

 artificial means or by natural agencies, a full crop of fruit 

 is produced, given normal conditions. In " Reversion " the 

 flowers become more or less abnormal in structure and artificial 

 pollination completely fails to produce a crop. 



Leaf Characters. With regard to the leaves, although the 

 general appearance of " reverted " foliage was familiar to all 

 growers, the precise symptoms by which one could detect 

 them with certainty were not clearly grasped. The method 

 of identification described by Mr. Lees is based on the fact 

 that the number of sub-main veins and marginal teeth are 

 fewer in " reverted " leaves, the decrease being small in 

 slightly " reverted " leaves and great in those which are badly 

 attacked. The examination should be confined to strong new 

 shoots, as spur leaves are apt to be unreliable. The successive 

 stages are found in the illustrations, No. 1 being a normal 

 leaf and No. 7 a very badly diseased one. It will be seen that 



* The " Eunning-off " of Black Currants : K. Wellington, E. G. 

 Hatton and T. Amos, Jour. Pomcloqy, Vol. II, No. 3. 



