18 BULLETIN 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 (PL 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. 
(PI. 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 (PL III, 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 and 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 
