SECTION H. — NATURE OF THE '* BLIGHT. 



23 



111 addition the young growing part of the cane still beneath the 

 sheaths of the green leaves exhibits an unnatural brittleness and liability 

 to break across in the internodes just above the level of the bud (eye) 

 and the ring of undeveloped roots. This break occurs frequently in 

 handling diseased canes for examination and also naturally in severe 

 cases, and is probably the immediate cause of the complete death of the 

 growing point frequently found in small and medium sized canes in a bad 

 attack. In Plates IV and V several of the dead shoots will be seen to 

 have broken off near the top in the manner indicated. 



Length and luidth of internodes. The internodes or joints which 

 are in the period of most rapid elongation are those bearing the outer 

 green leaves and those from which the leaves have recently fallen. As 

 a result of the great reduction of nutrition from roots and leaves during 

 an attack this increase of length does not take place and the green leaves 

 of the cane instead of separating from each other at the base, remain 

 crowded together and form a more or less fan-like arrangement of 

 leaves spreading at the tip, but close together at the base. This result 

 is distinctly seen in the tall cane to the left in Plate V. The 

 same reduction also occurs in the width of the internodes. This reduc- 

 tion in length and width is most cleai'ly visible in canes of medium size 

 as the largest canes have more reserve strength and show it less, while 

 the smallest shoots are killed so rapidly that there is no opportunity for 

 it to show (See Plate VI). 



When the canes begin to recover the still young internodes inci'ease- 

 in size but those which have matured and hardened during the attack 

 remain short and considerably reduced in width. 



These groups of short and narrow internodes remain visible on the 

 cane and form a convenient and easily available record of past damage 

 to the plant. Fig. 3 shows the successive lengths of the internodes in 



Fig. 3. 



Fig. 3— Diagram of leiigtlis of internocles in cane damaged by two broods of frog- 



hoppprs in 1919. 



December of a cane which had been damaged by froghoppers in both 

 August and October. Each of these two checks is visible by the 

 reduction in the internode length. The second check is more severe 

 than the first, as it was in this case increased by the advent of drought 

 at the same period as the second brood of froghoppers— the check thus 

 representing the combined result of the two. 



