1124 



Reversion of Blackcurrants. 



[Mar. , 



one counts the number of pointlets between C and X not 

 receiving submain veins, one finds the number to be two. as 

 against eight in the normal leaf. 



There are. therefore, well marked differences. So well 

 marked are they that the practical grower may say that he 

 could tell the difference by eye, without troubling to count. 

 Nevertheless, the method is of value, as can be shown by a 

 consideration of slighter cases of the disease. Fig. 2-7 

 represent advancing stages of attack. While Fig. 1 is normal, 

 Fig. 2 is slightly attacked, Fig. 3 more so, and so on until an 

 extreme type is reached in Fig. 7. At first sight, Fig. 2 appears 

 normal, especially as it possesses five submain veins. The 

 margin, however, is much more coarsely serrated than Fig. 1, 

 and has only four pointlets between C and X which do not 

 receive submain veins, as compared with eight in Fig. 1. It 

 has, therefore, a distinct touch of reversion in its make-up, and 

 any bush having such leaves is suspect. In Fig. 3, a further 

 stage is represented. Here, only four submain veins are 

 found, and the margin is still coarser, only two uninnervated 

 pointlets being present between C and X. In Fig. 4 — the next 

 stage — there are only three submain veins and two uninner- 

 vated pointlets. Fig. 3 and 4 are very common types in cases 

 of reversion. Frequently, no further stage in aberration of 

 leaf type is reached, but sometimes more extreme types are 

 produced, as in Fig. 5-7. where the submain veins are 

 successively reduced to two and a doubtful, two and one. In 

 Fig. 5. the third does not run to the margin, but is twined 

 round in an inward direction. The uninnervated pointlets are 

 reduced to zero in each case. Such types are frequently referred 

 to by growers as " oak leaves." The term is a convenient one, 

 but it must be understood that they grade into the more 

 ordinary types of reverted leaves, of which they are only 

 extreme cases. 



It will be observed that in Fig. 1-4 there is a successive 

 comparative elongation of the leaf, which is usually considered 

 by growers to be one of the characters of a reverted leaf. 

 The present writer, however, prefers not to lay emphasis on 

 this character, because though frequently it is a reliable guide, 

 a fuller examination of leaves in the field shows that it is 

 not completely so. One can find cases where reverted leaves 

 are quite broad in shape. The same applies to size. While 

 it is true that in the majority of cases reverted leaves are 

 smaller than normal, it is not always so. For instance, if a 



