520 Journal of Agricultural Research voi. xix, no. ro 



This interesting behavior was also noted in stools of crabgrass (Synr- 

 therisma sanguinalis) and foxtail (Chaetochloa lutescens). There were 

 no changes of growing conditions that could be correlated with these 

 apparent recoveries. In this connection it may not be out of place to 

 record that suckers from diseased stools of sugar cane and sorghum have 

 been observed to come up with no sign of mosaic. These instances are 

 by no means common, but several have been seen in both plants men- 

 tioned. 



INSECT TRANSMISSION OF CORN MOSAIC 



The manner in which corn mosaic is transmitted to healthy plants 

 and the relation of this disease to mosaic in other grasses was demon- 

 strated by the following experiments. 



Experiment i. — On March 12, 1920, 12 com plants of the variety 

 U. S. Select No. 182 were placed in each of two insect-proof cages. All 

 of the plants were from the same lot of seed furnished by the Office of 

 Cereal Investigations. The seed had been planted in one flat, and the 

 seedlings were replanted in 5-inch pots on the date of removal to the 

 cages. They were then 12 inches tall. About 12 individuals of Aphis 

 maydis were carefully removed by means of a small camel's-hair brush 

 from sorghum plants affected with mosaic to each corn seedling in one 

 of the cages. The sorghum plants had been infected by aphids from 

 mosaic sugar cane. Twelve aphids were transferred in the same way 

 from healthy sorghum to each of the com seedlings in the adjoining 

 control cage. On March 28, 6 of the 12 com seedlings in the first cage 

 showed typical signs of mosaic in the two youngest leaves. On April 6, 

 8 of the plants, or 66^ per cent, were typical cases. The 12 control 

 plants remained healthy up to the time of removal several weeks later. 



Experiment 2. — On April 6, 1920, 20 com seedlings, variety U. S. 

 Select No. 182, in 5-inch pots were placed in each of two insect-proof cages 

 in the greenhouse. Several specimens of Aphis maydis were transferred 

 from infected corn plants to each corn seedling in the first cage. Aphids 

 from healthy corn in another greenhouse were placed on each corn plant 

 in the second control cage, which was used as a control. On May 4, 7 of 

 the com seedlings in the first cage were found to be infected. On May 

 28, 15 of the 20 plants were observed to be unmistakable cases. The 

 aphids had increased enormously in both cages. Not a single case could 

 be found in the control cage, nor had any appeared up to June 25, 

 although the plants had been repotted twice and were approaching 

 maturity. 



These experiments demonstrate conclusively that provision is made 

 for almost unlimited dispersal of the vims through the medium of the 

 com aphis. There is no reason for supposing that transmission in nature 

 is limited to this insect or to this method. It is not yet known whether 

 the virus can survive the winter in seed, but experiments are now under 



