PECAN ROSETTE. 29 



pecan orchard of the Schley variety at Orangeburg, S. C. Final 

 notes were taken on a portion of these leaves at the end of 10 days, 

 while the remainder were left until September 9, 51 days later. 



In leaves of the primary stage, after 10 days, 17 yellow spots had 

 developed within 170 previously marked green areas. Of 130 yellow 

 spots already present, 11 in all had increased in size but only 2 con- 

 spicuously so. In slightly affected leaves of the secondary stage, 36 

 green areas had developed 13 yellow spots ; and out of 26 spots already 

 present 19 had increased in size, 15 of them decidedly. In the consid- 

 erably aborted leaves, 109 green areas had developed 137 new spots ; 

 and out of 270 spots present at the start 193 had increased in size, 70 

 of them by at least 50 per cent of their original diameter. These 

 leaves were all fully expanded at the beginning, since no appreciable 

 increase in size of blade could be discerned on comparing the leaflets 

 with their original tracings. The check leaves remained normal and 

 evidenced no ill effects from the presence of the India ink. 



Four uniformly pale leaves recently out of the bud and not fully 

 expanded at the first observation, at the end of 10 days, had de- 

 veloped a conspicuous green color around the margins and along the 

 veins, but had failed to develop further chlorophyll in the centers of 

 the areas between the lateral veins. These leaves were now typical 

 of the secondary mottled stage. 



In those leaves left for 51 days, 33 green areas in the primary stage 

 leaves had developed only 2 yellow spots. Of 180 spots already pres- 

 ent, 86 had increased in size, but only 15 decidedly so. In aborted 

 leaves of the secondary stage, 50 green areas had developed 17 spots 

 and of 66 spots present at the beginning 50 had increased in size, and 

 37 of them decidedly so. 



Most of the leaves of the primary stage were at the beginning older 

 and fully matured. The leaves of the secondard stage were fully ex- 

 panded, but for the most part soft and immature. It is thus apparent 

 that these yellow spots are not necessarily laid down in the bud stage 

 of the leaf or in a definite and unchangeable pattern, as may be the 

 case in certain heritable variegations. It is clear also that spots may 

 develop de novo even after expansion of the leaf blade and that those 

 already formed may increase in size, though less rapidly and fre- 

 quently after the leaf has fully matured. 



That yellow spots may increase in size was also shown by a study 

 of free-hand sections of fresh, living material. Here on the margins 

 of the spots an occasional cell was found which showed disorganiza- 

 tion of its internal structure on the side bordering the yellow area, 

 while that part of the cell contents toward the green periphery ap- 

 proximated the normal. (PI. XII, figs. E and K). Here again ap- 

 pearances suggest the outward diffusion of some toxin from a focal 

 center of its production. 



