Aug. :6, 1920 Mosaic Disease of Corn 519 



mosaic patterns in such leaves. In the youngest leaves, either the nor- 

 mal dark green or the pallid, affected tissue may predominate in a given 

 specimen, but the latter condition is most frequently met with. In such 

 cases the areas which remain normal are in the shape of broken or inter- 

 rupted streaks or lines extending in the general direction of the long axis 

 of the leaf (PI. 95), and the contrast in color between these areas and 

 the surroimding pallid areas is very decided. The streaks vary greatly 

 in size, ranging from mere points to elongated "islands" of dark green 

 2 or 3 cm. or more long and several millimeters wide. The margins of 

 such streaks may be straight or undulating. In most cases the mosaic 

 pattern is more prominent at the base of the leaf, where it diverges from 

 the leaf sheath. Where the normal dark green is predominant, the light 

 green, affected tissue appears usually as a very fine mottling or as 

 irregular elongated streaks on the darker background. From the fore- 

 going description it can be seen that the patterns vary considerably, and 

 yet they have certain general characteristics which make it almost impos- 

 sible to confuse this condition with any other affecting the leaves. 



Infected plants are always lighter in color than healthy plants. When 

 viewed from a distance such plants can be picked out with a fair degree 

 of accuracy on this account. The top of the plant is especially pale, 

 much more so than normal freshly unrolled young leaves. In some cases 

 the color becomes decidedly yellow. In this connection it must be stated 

 that the pallid color referred to heretofore as characteristic of the dis- 

 eased areas is not a yellowish green but a lighter or more dilute tint of 

 the normal green. In plants which become markedly yellow a decided 

 stunting of the whole plant takes place. At no time has a case been 

 observed to terminate fatally, but certainly considerable injury results 

 from the lack of functioning chloroplastids, and where a large percent- 

 age of the plants are affected the loss due to decreased size of ears is 

 appreciable. When infection takes place early in the growing season, 

 partial or complete sterility of the ears results. This serious feature of 

 the disease was first noticed in Louisiana in 1920. In May, 1920, the 

 writer tagged 20 diseased and 10 healthy plants in a field of White Creole 

 com. The diseased and healthy plants were equally vigorous to all 

 appearances at that time and were in the same rows, alternate diseased 

 and healthy plants in the same row being selected as far as it was practi- 

 cable. When the crop was harvested in August, 17 of the diseased plants 

 were found to be completely sterile, while 3 of them had set a few scattered 

 kernels. The 10 healthy plants were normal, excepting for slight com 

 earworm injury, and produced large well-filled ears (PI. 96). 



During the course of experiments in the greenhouse several cases of 

 apparent recovery have been observ^ed. Plants which became infected 

 and exhibited the typical symptoms resumed their normal color after 

 several weeks. These plants were held under observation until the ears 

 were mature, but there was no recurrence of the mosaic symptoms. 



