MOSAIC OF SUGAE CANE AND OTHER GRASSES. 13 



various sugar-cane experiment stations, but the list includes also 

 practically all of the commercially esteemed sorts grown for the mills 

 on a plantation scale. 



So far as can be learned, none of the varieties grown in Java is 

 truly immune, but a high degree of resistance or tolerance of the 

 disease has been observed in the favorite Java seedling canes grown 

 in Porto Rico, a probable explanation of which has already been given. 

 Only Java 56, 100, 228, and 234 have been seen by the writer in 

 Porto Rico, but all of these, though 100 per cent of the individuals 

 were affected, made a thrifty growth and produced apparently normal 

 stalks. The leaves arc not noticeably yellowed, but on the contrary 

 appear to be of uniform dark-green color when viewed from a dis- 

 tance. Close inspection, however, shows the characteristic streaks, 

 but the diseased areas are very little lighter than the normal areas. 

 Probably the damage done to an individual plant is slight, but the 

 aggregate damage to all of the individuals in a field is a measurable 

 quantity and has been shown to be quite considerable in Java. In 

 the different varieties all degrees of tolerance are exhibited, ranging 

 from the highly resistant Java canes down to the soft white Otaheite 

 or Bourbon cane, which is so severely injured that the cane is hardly 

 worth milling. In addition to the conditions which might be termed 

 varietal tolerance of the disease, some varieties exhibit decided and 

 rather constant differences in the percentage of individuals that 

 become affected under the same conditions. This is brought out in 

 variety-row tests where the same varieties have been planted at 

 several points in the same field. Under these conditions it has been 

 found that some varieties will show a 100 per cent infection of the 

 individuals in all of the rows, while in others perhaps only 60 per cent 

 of the plants will be diseased in each of the separated rows or plats. 

 It seems reasonable to suppose that all varieties were equally exposed 

 to the contagion in such situations. This fact indicates a possibility 

 of resistant strains among the individuals of a variety. 



The Rayada or Striped cane and the Crystalina or White Trans- 

 parent, the two favorite varieties in Porto Rico, are severely injured. 

 Yellow Caledonia is grown on a large scale in some localities, and 

 plants of this variety killed by the mosaic disease have been observed. 

 This is quite unusual, since attacked plants of most varieties become 

 badly stunted but do not die. All seedling canes from Demerara 

 and Barbados grown in Porto Rico are attacked. Seedlings of the 

 Insular and Federal agricultural experiment stations likewise are all 

 affected, as are the seedlings originated at Centrals Guanica and Fa- 

 jardo. Among the varieties planted commercially to a limited ex- 

 tent the Bambu, Cavengerie, Morada, and, in fact, all the broad- 

 leaved canes have proved to be susceptible. 



