26 BULLETI2Sr 1038, U. S. DEPABTMENT OF AGRICULTURE. 



palisade or spongy cell and many of the guard cells were, however, 

 filled with starch as in leaves collected at sundown (PL VII, fig. A) . 



Mottled leaves of all sizes collected at night showed the green por- 

 tions gorged with starch (PI. 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. 



Wherever 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, 



