PECAN KOSETTE. 27 
which later recedes from the cell wall (PL XII, fig. J), and at last 
the whole cell collapses and shrivels. 
The deposition of crystal aggregates of calcium oxalate is char- 
acteristic of pecan leaves (PL VII, fig. B). These crystals begin 
to form in giant binucleate cells of the palisade just after the young 
leaf emerges from the bud. Finally the protoplasmic contents dis- 
appear, and the crystal aggregate nearly fills the cell. These crystal 
aggregates are distributed with considerable regularity in the healthy 
leaf and in the majority of cases one to each vein islet (PL X, fig. E). 
In the yellow spots of the secondary stage of the disease, on the other 
hand, their formation and distribution vary widely. At the focal 
centers in severe cases. few or no crystals at all are formed, whereas 
in the surrounding green parts they are often far more numerous 
and sometimes larger than in the comparable healthy leaf. 
Averaging a large number of counts in cross sections of green 
parts of diseased and normal leaves of the Frotscher variety col- 
lected at Thomasville, Ga., it was found that in the normal leaves 
20 crystal aggregates occurred to every 100 vein islets observed in 
section, while in the diseased leaves 60 crystal aggregates were found 
to every 100 vein islets. In Van Deman leaves collected at Baconton, 
Ga., there were 16 crystal aggregates to every 100 vein islets in the 
healthy leaves as compared with 54 in the diseased leaves. Further- 
more, after all due allowance for differences in cortical area of the 
diseased and healthy leaves compared, a much larger number of 
these crystals was found in the cortex of petioles and midveins in 
rosetted leaves. In view of the fact that waste organic acids usually 
accompany carbohydrate formation (57, p. 173) these results are 
significant. Since growth at the periphery of the yellow spots 
in the secondary stage is often abnormally active, as is shown by 
the size of the cells, an unusually large accumulation of such or- 
ganic acids would naturally be expected to take place in that region. 
Conversely, with the reduction of chlorophyll formation and assimi- 
lation in the centers of the spots a smaller production of such acids 
would occur. 
Development of the shield-shaped resin glands occurring mostly 
on the lower surface of the leaves is also profoundly affected by the 
disease. On the normal leaf these glands are rather regularly and 
sparsely distributed over the surface of the blade and contiguous 
to the veins and veinlets. In diseased leaves of the secondary stage, 
on the contrary, the focal centers of the yellow spots are often 
thickly covered with these resin glands both contiguous to the vein- 
lets and well within the vein islets themselves. The more severe 
the general effects of the disease the more numerous were these glands 
found to be, until in places where the tissues were practically de- 
