Abstract1. The "eye spot" disease which is caused by Helminthosporium sacchari Butler is serious on certain varieties of sugar cane in Porto Rico. 2. It is most severe on F.C. 306 and D. 109 with H. 109 as a poor third. The Uba and P.O.J. canes are most resistant. 3. The susceptibility varies with leaf structure, the higher the fiber content the greater the resistance. However, there appears to be some slight correlation with sucrose content. 4. The young leaves are more susceptible than the old leaves; the bases and upper surfaces more susceptible than the tips and lower surfaces. 5. The spores and sporophores germinate readily in water and penetrate the leaf without regard to the stomata. The greatest mycelial growth is in the parenchyma tissues. The spores are borne more abundantly on the lower than on the upper surface of the leaf. 6. The disease is most severe during the cool, wet months of the year. Temperature appears to be the most important environmental factor. 7. The most satisfactory control for Porto Rico at his time consists in the use of resistant varieties.
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