68 Leaf Character in Reverted Black Currants 



ABSTRACT. 



1. A means is indicated whereby reverted leaves may be identified 

 even in very slight cases or where the leaves have almost regained 

 normality. 



This method depends (a) on counting the number of submain veins 

 running from the midrib to points in the margin, and (6) on observation 

 of the margin points, which also may if necessary be reduced to a 

 numerical basis. 



2. That reverted leaves may be produced by artificial means, but 

 that this reversion is of a temporary character. In each case examined 

 the plant appeared to be under a special stimulus to growth. 



3. Cases in the field were examined in detail in three respects, namely 

 {a) leaf vein number, (6) mite infected buds, and (c) leaf margin. Three 

 classes could be distinguished: (a) normal healthy, (6) simple reverted, 

 and (c) mite infected (reverted). These corresponded with three factors 

 which appeared to be acting: {a) seasonal factor, (6) reversion factor, 

 and (c) mite factor. Furthermore, since "oak leaf" is an advanced stage 

 of reverted leaf and is always associated with mite, the chances are 

 that reverted leaves when found without "oak leaf" owe their existence 

 in some way or other to the mite factor either patently or latently. 



EXPLANATION OF TABLES I AND II 



In the columns headed "Veins" the numbers represent the number of submain veins 

 from the midrib running to a point in the margin. The veins on only one side are counted, 

 but where an extra one appears on either side the sign + is used after the numeral. Simi- 

 larly the sign + is used where the topmost vein is doubtful. Thus 3 + indicates either 

 ;i on one side and 4 on the other or that on one side there were 3 clearly defined veins 

 and one doubtful. 



The words "Missing" and "Dam." indicate that the leaf was absent or damaged. 



In the column headed "Mites" the approximate number of mites in the particular 

 axiliary bud is given. "Mod." signifies a moderate amount and "BB" that a big bud was 

 already forming, this being an indication of heavy infestation. The last number refers to 

 the terminal bud. In the column headed "Leaf margin" the character of the leaf margin 

 is shown in accordance with the description in the text. 



{Received August 3Is^, 1921.) 



