28 BULLETIN 1038, U. S. DEPARTMENT OF AGRICULTURE. 



funct or bordering wounds where such tissues had fallen out, they 

 presented a continuous, rough layer of glandular shields. Examina- 

 tion of ordinary leaf wounds such as those made by insects showed 

 no such abnormal development of resin glands. These conditions 

 have been frequently observed in the general examination of leaves 

 collected during several seasons and in different varieties and locali- 

 ties. Furthermore, using a simple binocular microscope, observa- 

 tions have been checked up by exact counts. For example, counts 

 were made of the numbers occurring in a single field in different 

 parts of 10 norn^al leaves of the Frotscher variety collected at 

 Thomasville, Ga. (1916), and in the yellow areas of 10 comparable 

 rosetted leaves. The average for normal leaves was 8 to a field, 

 while in the diseased leaves there were 92 to a field. In a lot of the 

 Schley variety collected at Orangeburg, S. C. (1920), the average for 

 healthy leaves was 43 and that for comparable yellow areas of 

 diseased leaves 212 to a field. Similar results were found in material 

 collected at Belleview, Fla., and at Baconton and Cairo, Ga. In some 

 older spots of the secondary stage these resin glands were so closely 

 packed together that counting was impossible. 



This increased development of resin glands is characteristic of 

 many halophytes and xerophytes and in these cases apparently bears 

 some relation to the condition of physiological dryness. Further- 

 more, Tschirsch (80) has demonstrated that the secretion of resin 

 is produced within the cell wall itself just below the cuticle. This 

 region he calls the " resinogenous layer." Nutrient substances and 

 water pass out of the protoplast into this resinogenous layer, to be 

 there further molded into the final product, resin. This process, 

 then, is participated in by both protoplast and cell wall and necessi- 

 tates loss of material from both and a final breaking down of the 

 cell wall itself. In pecan rosette this abnormal developmient of resin 

 glands is then probably to be connected in some way with the gradual 

 and general degeneration of the cells involved. 



In order to determine whether new spots may be formed after the 

 full expansion of the leaf and whether yellow spots already formed 

 may increase in size, resort was made to careful field observation and 

 microscopical study of fresh living material. On July 20, 1920, at 

 Orangeburg, S. C., the outlines of several hundred spots on 56 dif- 

 ferent leaves of both primary and secondary stages were carefully 

 traced with India ink on the upper surface of the blade. At the 

 same time the outline of one leaflet on each leaf was traced on paper 

 for comparison with its size at the end of the observational period. 

 Furthermore, nonmottled areas of diseased leaves were marked in a 

 similar way; and finally also certain areas of normal leaves were so 

 marked as a check on possible injury by the India ink. These leaves 

 were located on one normal and five rosetted trees in a 45-acre 



