26 BULLETIN 1038, U. S. DEPARTMENT OF AGRICULTURE. 
palisade or spongy cell and many of the guard cells were, however, 
filled with starch as in leaves collected at sundown (PI. VII. fig. A). 
Mottled leaves of all sizes collected at night showed the green por- 
tions gorged with starch (PL XI, fig. C). The plastids of the pali- 
sade and spongy cells were not only filled to the periphery but swollen 
as if almost bursting with their accumulation of starch. Toward 
the center of the yellow spots (secondary stage) the chlorophyll 
bodies are of less and less frequent occurrence until at the center only 
an occasional starch-filled plastid is to be found (PL VII, fig. D). 
In these areas where the effects of the disease have been in operation 
from the early stages of bud growth the inhibitory influence has 
affected not only tissue differentiation but has also prevented normal 
development of the plastids. 
Mottled leaves collected before sunrise the following morning ap- 
peared the same as those collected at night (PL XI, fig. D). As far 
as could be determined from the iodin stain, no translocation at all 
had taken place during the night. Palisade cells, spongy cells, and 
guard cells of the green areas were full of starch, and the occasional 
plastids in the bundle sheaths of the veins were also gorged. 
The nonmottled, but greatly aborted leaves, showed this gorging 
of the plastids over the whole lamina. The starch sheaths around 
the midveins were also black with starch. As in the other diseased 
leaves the plastids appeared as full of starch in the early morning as 
at the end of a sunny day. 
TTherever plastids are present in either stage of leaf mottling the 
first sign of disease in these bodies consists in a gradual loss of the 
green chlorophyll. In the healthy living cell of both palisade and 
spongy parenchyma the plastids are plump and of a livid green color, 
while the nucleus is plainly visible as a grayish, more or less cen- 
trally located body with definite outline (PL XII, figs. A and C). 
As the disease progresses these chlorophyll bodies first lose their 
green color (PL XII, fig. D) , then both nucleus and plastids begin to 
break down (PL XII, figs. B and E to H) , first losing their definite- 
ness of outline, or becoming fragmented or appearing as if eaten away 
at the periphery. Later all the visible remains of the cell structures 
consist of globules, probably fatty, and darker-colored granules of 
various shapes and sizes irregularly distributed throughout the cell, 
with all appearance of disorganization. "With ferrous salts many of 
the brownish granules gave the reaction for tannin. In cases of 
severe attack the entire tissue within these yellow areas later becomes 
reddish brown and collapses (PL I. fig. 3). In reaching this end 
stage the tannin degeneration products here described gather into 
larger and larger floccules (PL XII. fig. I) until finally the cell may 
be filled with a more or less homogeneous reddish brown matrix, 
