60 Leaf Character in Reverted Black Currants 



plant is subjected to a special growth stimulus, then a similar reduction 

 should be expected, though less in degree, when the plant is under the 

 normal growth stimulus which occurs under optimum conditions of 

 growth. This is apparently what happens. At the same time the veins 

 were never reduced below five, which may be taken as the lowest figure 

 for normality, nor was the margin in the least reverted. 



Case 2. While case 1 illustrates a leaf series of a normal shoot, case 2 

 represents the same for a reverted one. The twig indeed came off the 

 same bush but from the reverted half. In this case the basal leaves were 

 normal with six veins, but the successive leaves showed greater and 

 greater reduction of veins and increase of reversion until the figure two 

 was obtained for the tenth leaf (Table II and Graph 2). At the end of the 

 graph there is a sUght tendency for the vein number to recover, but by 

 June 29th the growth season had not nearly finished. The graph shows 

 therefore a much more marked descent than in Graph 1 , but of the same 

 order. Here therefore there appear to be two factors working, reversion 

 and the normal drop due to growth stimulus. 



Case 3. This was a shoot from a cutting from a seedling. All the rest 

 of the bush was normal. No mite could be found in any of the lateral 

 buds or in the terminal. Reference to Table II shows that the reversion 

 effect came on fairly suddenly at leaf 7 where there was a sudden drop 

 to 4 + in veins and the margin first showed distinct signs of reverting. 

 This continued till leaf 14 when the margin began to show signs of 

 improvement and by 16 was practically normal again. The vein number 

 follows in the same line. Graph 3 shows much the same condition as 

 Graph 2 except that being examined later, on July 7th, more of the 

 terminal rising portion of the curve was obtained. Here therefore is 

 a shoot that started normally and finished normally but in between was 

 strongly reverted. 



Case 4. This was a shoot from a bush that had been cut back for 

 grafting and the shoot came from' the stock. Again here the first leaf 

 was normal, but the reversion was very sudden. Bud No. 2 contained 

 three mites, but except for this the shoot was completely free from mite 

 infection. The recovery in leaf vein number was fairly quick, the normal 

 figure of five being attained by the ninth leaf after which there were 

 only very small variations. The margin recovery was neither so quick 

 nor so complete, there being indication of reversion here even in the 

 last leaf formed. 



Cases 5 and 6. Both these were very strong shoots, case 5 being a 

 shoot from the base of a bush cut back for grafting and case 6 a shoot 



