Abstract1. The symptoms of mosaic are more conspicuous on actively growing than on slow growing plants; and on the new than on the old leaves of a diseased plant. 2. The light areas of a diseased leaf are slightly thinner than the green areas. 3. The green areas correspond in every way to the leaves from healthy plants of the same age and variety. 4. The cells in the light area of a diseased leaf are slightly less in size than those in the green areas. 5. Intracellular bodies were difficult to find but corresponded quite well with those reported by Kunkel. 6. The host nuclei were usually very much enlarged in the diseased tissues, especially in the tissues of the leaves. They were frequently very irregular in form and it was very difficult to find intracellular bodies associated with them. 7. The chloroplasts were smaller and fewer in number in the mosaic than in the healthy tissues. 8. The internal cavities in both stems and leaves start with a disintegration of the cell walls.
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