18 BULLETIISr 1038, U. S. DEPARTMENT OF AGRICULTURE. 



tissue occasionally fail to develop ; as a result of subsequent growth 

 stretching in continguous tissues the blade becomes dotted with 

 smooth-margined holes suggestive of healed insect punctures. 



During the early course of the disease, or in cases of very slight 

 attack, yellow mottling may be the only external sign (PI. I, fig. 4) , 

 the size, shape, and texture of the leaves appearing normal. This 

 primary stage is less characteristic than the secondary stage, but 

 here also the chlorotic mottling is confined to areas between the prin- 

 cipal side veins. The regions along the veins and leaf margins 

 remain green. With advance of season the chlorotic areas of both 

 primary and secondary stages often turn a dark reddish brown. 

 (PL I, fig. 3.) Signs may appear over the' whole tree at once, but 

 frequently only one or more branches on a tree are affected at first. 

 Early indications of rosette often consist in the appearance late in 

 the season of a few mottled leaves near the tip of one or more 

 branches, the remainder of the tree appearing normal. Leaves de- 

 veloping signs earlier in the season often present a general bronzed 

 appearance during late summer and fall, and particularly is this 

 true under conditions of drought. 



Later, where the branches also become affected, there is considerable 

 reduction in growth, so that the aborted leaves become clustered 

 together on a shortened axis, giving the characteristic bunched appear- 

 ance of the foliage at this stage (PI. Ill, figs. A and C). It was 

 this close bunching of the leaves that led Orton originally to apply 

 the name "rosette" to the disease (56, p. 151). A few nuts are 

 often borne on branches not too severely attacked, but they are 

 usually malformed and reduced in size. 



Affected trees may continue thus for several years, or they may 

 appear to recover completely after showing moderate signs for 

 one or more seasons. However, in severe cases where the signs have 

 spread over the whole tree and in some instances where only one or 

 more branches are severely attacked, the affected branches begin 

 to die back from the tip during the latter half of the growing season. 

 At first brownish spots and streaks develop in the chlorophyllous 

 inner bark, and these dead areas increase in size until the bark and 

 cambium are disorganized aiid the end of the twig or branch dies. 

 This staghorn phase is followed during the current and subsequent 

 seasons by development of abnormal numbers of shoots from dor- 

 mant and adventitious buds. Usually in young rosetted trees the 

 first shoots of the season are abnormally large and succulent, and the 

 leaves are dark green and larger than normal. This is probably in 

 part due to the severe pruning induced by the staghorn phase, since 

 similar results are obtained by severe artificial pruning during 

 earlier phases of the disease. Toward midseason, however, the mot- 

 tling begins to appear and the later developed leaves present the 



