SECTION II. — NATURE OF THE '' liLIGIlT." 21 



Stage I. (Plate II. fig. la). Within a day or two of the sucking 

 of the adult froghopper at any point of the leaf the first indication of 

 injury appears as a pale area surrounding the puncture and elongated 

 slightly in the diyection of the axis of tlie leaf. This decolourized 

 area is more transparent than the rest of the leaf and is readily seen 

 when the leaf is held up to the light. 



It increases considerably in size particularly in the direction of the 

 axis before the next stage is reached, and becomes a long narrow streak 

 on the leaf, in the centre of which the original punctm^e is sometimes 

 visible as a small brown spot. The elongation takes place both above 

 and below the original puncture, but as a general rale is slightly more 

 rapid towards the tip of the leaf than towards the base. 



This first stage streak is seldom more than one-tenth of an inch wide 

 and may reach three inches in length. A streak 0"5 of an inch long 

 was 005 of an inch in width. Others from 2'5 to 3 inches long were 

 about O'l of an inch in width. 



Stage II. (Plate II fig. \h). After a few days the centre of the pale 

 streak becomes discoloured by a reddish brown pigment usually appear- 

 ing first as a number of small points round the original puncture and 

 producing a finely mottled effect. This discoloration spreads rapidly 

 up and down the streak, which becomes red brown tliroughout, while only 

 the newly invaded tissue round the edge remains pale. 



Frequently the red pigment forms very narrow hair-like streaks 

 which run for a considerable distance up and down the leaf along a 

 vascular bundle. 



The red colour usually begins to appear when the original streak, is 

 about 1"5 to 2 inches long and, concurrent Avith its development the 

 injury spreads both laterally and longitudinally, so that the second stage 

 may reach 5 inches in length and about 0'175 or 0*2 inches in width. 



Actual measurements of streaks of this stage are : 1"5 x 0*1 inch (red 

 pigment just appearing) ; 2"5 x 0"1 (of this length 1 inch was a hair-like 

 line projecting at the outer end) ; 2'o x 0'175 ; 3 x 0"05 ; 3"G x 0'15 ; 

 4*5 X O'lVo (2'5 of this was a red hair-like streak) ; 5 x O'.l, very long and 

 narrow, red hair-like line distinct. 



Stage III. (Plate II. fig. Ic). In this stage the destruction of the^ 

 tissue round the point of injury begins to be complete, the centre of the 

 red area dries out and becomes silvery brown in colour and opaque to 

 transmitted light. This dead area spreads until it occupies the greater 

 part of the streak, leaving only a narrow border of red edged with pale 

 green where it is still encroaching on the undamaged tissue. The 

 streak at this stage is usually more than two inches long and may reach 

 a length of from four to six inches and a width of from O'lo to 0"25 

 of an inch. 



If the original punctures are close together the separate streaks join 

 up into large dead areas on the leaf which I have found it convenient 

 sometimes to record as stage lY, but which i-eally only represents a 

 number of overlapping streaks of Stage III. 



The total destruction of leaf tissue resulting from a single puncture 

 by a froghopper may thus exceed half a square inch, and as a stool of 

 cane may have fifty or more adults, each of which will suck at several='= 



* Recent experiments show that on an average two streaks develop for each 

 froghopper per night. 



