SUMMARY. 15 f 



an almost imperceptible point, the damaged area may reach five inches 

 in length and a quarter of an inch in width forming a long discoloured 

 streak on the leaf. The centre of this area finally dies completely 

 (PI. TI). If these streaks are numerous they may join up to form large 

 dead areas on the leaf. It follows that the injury to the leaf, and so to 

 the plant, may continue to increase after the brood of froghoppers has 

 passed, (p. 20). 



The stem is only indirectly damaged by loss of food from the 

 damaged roots and leaves. The growing point is frequently stained 

 with red internally, especially' at the young nodes ; small pockets of 

 gum are sometimes found, and an unnatural brittleness frequently 

 causes the cane to break off just above one of the upper nodes. The 

 internodes or joints which should be increasing in length and width, 

 remain shorter and thinner than usual and harden while still in this 

 condition, recording on the growing cane the check that the plant has 

 received. Thus from the lengths and widths of successive internodes on 

 a fully grown cane past attacks can be determined (fig 3). The 

 shortening of the upper internodes causes the leaves to be crowded 

 together in a fan-like arrangement. In addition the eyes near the top of 

 the cane frequently send out shoots, and adventitious roots are developed 

 from the joints near the ground, (p. 22). 



The roots are damaged both by the sucking of the nymph, by the 

 root fungi usually associated with blight, and by the unfavourable soil 

 conditions nearly always found in fields liable to attack. The root 

 system is poor and the plant can be pulled from the ground with com- 

 parative ease. (p. 24). 



The blighted canes contain less sap than healthy ones, but often a 

 higher sucrose percentage. The sucrose is said to be more easily 

 inverted in sap from diseased canes, and the sap is frequently acid. (p. 24). 



The different parts of the stool are usually damaged inversely as 

 their size and vigour. The smallest shoots are killed, the medium sized 

 ones severely checked, and the larger only slightly injured except in 

 cases of sevei-e continued damage, (p. 25). 



As the brood passes the canes are able to send out undamaged leaves 

 and gradual recovery sets in. This will vary according to the extent of 

 the original injury. The length of time taken for a plant to produce a 

 new set of leaves is however longer than the time between successive 

 froghopper broods, and as a result the cane after one attack is in a 

 weaker condition to withstand a second. This probably accounts for 

 the greater damage caused by a second brood even when its numbers do 

 not appear to be greater than the first, (p. 25). 



The greatest intensity of the blight is about two to three weeks after 

 the height of the froghopper bi'ood, but the total damage varies gre itly 

 from year to year and from place to place, (p. 27). 



Uncomplicated froghopper attack is distinguished from uncompli- 

 cated root disease by the presence of the brown streaks on the leaves. 

 Froghopper injux-y is never confined to a few isolated stools as 

 occasionally occurs in the case of root disease. Root disease further has 

 not the periodic nature of froghopper blight. The blight resembles in 

 symptoms the Sereh disease of the East, but does not become steadily 

 worse each year as with the latter. The resemblance of the symptoms is 

 largely accidental and Sereh does not occur in Trinidad. Certain fungi 

 make discoloured spots on the leaves of the cane. The chief of these are 

 the Eye-Spot (Hehninthosporiiim) and the Ring-Spot {Leptosphaeria), 

 but the marks are quite distinct from those of froghopper injury. The 

 Eye-Spots are small, seldom more than half an inch in length, and have 

 only been found up to the present on one variety of cane, D 109. The 

 Ring-Spots are purplish-brown in colour with a paler centre and almost 



