80 
Proceedings of the Royal Society of Edinburgh. [Sess. 
M. ribis is known to feed upon black currant and gooseberry, but it is 
less damaging to these than to Ribes rubrum. In 1918, black currant and 
gooseberry growing beside observation bushes of red currant in my garden 
were unaffected. A colony artificially founded upon gooseberry died out 
in the first generation after transference ; and the third generation on black 
currant resulted in a swarm of winged forms which left the bushes at the 
end of May after producing a slight curling of the leaves. 
The only effective remedial measure against M. ribis is to spray the 
bushes with soft soap, or nicotine solution, or paraffin emulsion in April as 
soon as the buds open. Where possible, it is advisable to pick off the 
blistered leaves by hand, as these afford shelter to the pest ; and in case any 
aphides escape the first spraying, a second should be given early in May. 
Theobald recommends spraying the bushes with paraffin jelly early in 
October, to destroy the sexuales ; but as my observations go to show that 
currant-reared sexuales may appear in September, and be succeeded in 
October by an immigration from the summer host plant, this method is 
uncertain, for oviposition may have taken place before the remedy is 
applied, and the egg is impervious to the wash. Ridding the neighbouring 
ground of such weeds as Lamium, Polygonum , and Veronica, which 
harbour the aphides in the late summer, might also be beneficial, but little 
reliance can be placed on this method of control. 
The Dimorphism of the Red Blister and Green Leaf Forms. 
Myzus ribis has already been so exhaustively described by Kaltenbach 
(16), Flogel (10, 11), Patch (23), and others, that an account of the general 
characteristics of the parthenogenetic forms is unnecessary here. But in 
1918 I noticed a dimorphism in this species, which, though it has not 
been treated as such by other observers, seems sufficiently remarkaole to 
be described in detail. 
When dealing with four fundatrices in April, a difference had already 
appeared between two which were found upon red-blistered leaves and 
two taken from green undistorted leaves. Briefly, the stem mothers on 
the former were pale yellow, with round abdomens, while those on the 
latter were green and more oval in shape. One of each form was chosen 
for breeding the generation series, and the other two were mounted alive 
in balsam and measured. 
The breadth of the head is taken as the standard in calculating the 
proportions of the fundatrices, as subsequent results with the succeeding 
apterous generations, have shown that it is the least variable of the 
dimensions chosen for measurement. It can be seen from Table A that 
