134 Journal of Agricultural Research voi.xix, no. 3 



and consequently was not determined. On June 3, 1919, all five of the 

 Lahaina cane plants from Dr. Smith's greenhouse showed unmistakable 

 incipient signs of mosaic. Two weeks later all were well-developed cases. 

 Experiment 2. — On July 3, 191 9, 15 healthy cane plants of the 

 Lahaina variety, 7 months old, were removed from the greenhouse in 

 Washington to the "pesthouse" at Garrett Park. Five were placed 

 within the house unprotected as before, and 5 were placed in each of two 

 insect-proof cages. On July 22,4 of the exposed plants showed incipient 

 signs of mosaic. On August 2 the remaining plant showed evidence of 

 being infected, and a week later all the exposed plants exhibited well- 

 advanced leaf symptoms. At this time the 10 control plants in cages were 

 perfectly normal and continued so until they were used in another 

 experiment two months later. 



Experiment 3. — Seeds of sweetcorn (Yellow Bantam variety) and 

 sorghum (Sugar Drip, Early Amber, and Japanese Ribbon) were planted 

 on August 13, 1 918, in the Garrett Park quarantine greenhouse. They 

 germinated and grew slowly during the winter, then more rapidly in the 

 spring. A number of volunteer grasses that came up as weeds in the 

 greenhouse were allowed to mature. All these plants soon became heavily 

 infested with corn aphis. Sorghum seed from the same lot was planted 

 in a greenhouse at Washington. On May 7, 1919, a few mottled leaves 

 appeared on the sorghum plants at Garrett Park. Examination of the 

 wild grasses revealed the typical streaking and mottling in practically 

 every stool of crabgrass {Syntherisma sanguinalis) , foxtail (Chaeiochloa 

 lutescens) and Panicum dichotomiflorum. Other wild grasses in the 

 greenhouse were normal. At this time the sorghum control plants in the 

 Washington greenhouse and the wild grasses of the same species outside 

 the greenhouse at Garrett Park showed no signs of mosaic, nor did they 

 show any evidence of mosaic during the remainder of the summer. 



Experiment 4. — On August 7, 1919, about 50 adult individuals 

 of the sharp-headed grain leafhopper {Draeculacephala molipesy col- 

 lected two days previously on mosaic-diseased sugar cane at Audubon 

 Park, New Orleans, La., were placed in a cage with 5 healthy cane 

 plants at the Garrett Park greenhouse. The leafhoppers immediately 

 began feeding on the healthy cane. No infection was evident after two 

 months. 



EXPERIMENTS AT WASHINGTON 



During September, 191 9, nearly all experiments were transferred to 

 greenhouses especially prepared to receive them at Washington. Venti- 

 lators of the 2-story greenhouse, formerly used by Dr. Smith for bananas, 

 were screened with physician's cloth ; and the diseased cane plants of all 

 varieties were removed to it from Garrett Park. A greenhouse in 

 another range, separated by a roadway from the first, was screened; and 



' Identified by Mr. T. E. Holloway, Bureau of Entomology, United States Department of Agriculture. 



