. MOSAIC OF SUGAR CANE AND OTHER GRASSES. 17 



as it does from a common starting point, there is seen to be nothing 

 to substantiate this claim. 



Only a few specific observations of infection may be cited in the 

 limited space available. In October, 1918, healthy seed of about 80 

 varieties was brought into the infested area from disease-free regions 

 in order to determine whether any natural immunity existed among 

 the varieties present in Porto Rico. This seed was planted at the 

 Santa Rita estate, near Yauco. When the seed germinated, the 

 young plants were seen to be healthy and normal, but within six 

 weeks to two months practically every plant of all varieties with one 

 exception (the Japanese Kavangire) showed the unmistakable symp- 

 toms of mosaic. This was a clear case of secondary infection from 

 the fields of diseased cane surrounding the test plat. 



At Santiago de las Vegas, Cuba, about 200 seed pieces of Java 228 

 cane imported from Tucuman, Argentina, were planted in two rows, 

 and two rows of the native Crystalina cane were planted beside them. 

 The Java cane was 100 per cent infected when it came up, the cut- 

 tings having come from diseased parent plants. When this planting 

 was examined in June, 1919, 75 per cent of the Crystalina plants 

 were characteristically diseased. The Crystalina seed pieces had 

 come from a field which was minutely searched and found to be en- 

 tirely free from disease. No other cases were found in the entire 

 region, in fact, with the exception of a single stool of L 511 imported 

 from Louisiana. 



In July, 1919, a field of D 74 stubble cane, grown for sirup near 

 Cairo, Ga., was found to be healthy with the exception of one corner 

 near the kitchen garden, where about 80 per cent of the plants had 

 the mosaic. Investigation revealed the fact that a patch of green 

 chewing cane had been growing adjacent to the D 74 at that corner 

 during the preceding year. The green cane was found growing else- 

 where on the farm this year, and examination showed that every 

 plant had the mosaic disease. Clearly the D 74 had become infected 

 last year, the disease had survived the winter in the stubble, and the 

 shoots were diseased when they appeared again. 



At Washington, D. O, 17 varieties of cane, all diseased, are growing 

 in an insect-proof quarantine greenhouse. 1 From time to time 

 healthy sugar-cane plants in pots have been taken into the greenhouse 

 and left exposed to the contagion. Invariably they show the incip- 

 ient symptoms of the disease on the average in 17 days, proving that 

 the incubation period is from two to three weeks. As has been men- 

 tioned elsewhere, sorghum and wild grasses taken into this greenhouse 

 have also become infected. Much more evidence of this kind could 

 be adduced, but it is believed to be sufficiently clear that infection 



1 Insects were present in the greenhouse. 



