272 Journal of Agricultural Research voi. xvn. No. e 



SUMMARY 



(i) Mosaic of the Irish potato has become well distributed over the 

 United States. 



(2) It has a decidedly detrimental effect upon yield. 



(3) It produces characteristic symptoms upon the aerial parts of the 

 plant, especially on the foliage. These symptoms may be modified or 

 obscured by differences in environment or variety. 



(4) Tubers of diseased plants carry the disease. 



(5) Grafting a healthy scion upon a diseased stock, or a diseased scion 

 upon a healthy stock, may result in the development of the disease by 

 the originally healthy scion or stock. 



(6) Mosaic may be transmitted by transferring juice from a diseased 

 plant to a healthy plant. 



(7) At least two species of aphids can transmit potato mosaic, whether 

 the aphids are transferred artificially or disperse naturally, 



(8) Mosaic apparently tends to increase the sugar content of the leaves 

 and to reduce their starch content. 



(9) Hill selection has not proved successful for maintaining healthy 

 stock when practiced in fields having a considerable number of mosaic 

 plants. 



(10) Roguing or eliminating mosaic plants before aphids become abun- 

 dant is indicated indirectly by certain experimental evidence here presented 

 as being helpful and also has been found actually efficient for checking the 

 spread of the disease. It appears also that isolation of the rogued seed 

 plot is very desirable. 



LITERATURE CITED 



(1) AiLARD, H. A. 



191 7. FURTHER STUDIES OP THE MOSAIC DISEASE OP TOBACCO. In JoUT. AgT. 



Research, v. 10, no. 12, p. 615-632, pi. 63. 



(2) D00UTT1.E, S. P. 



1916. A NEW iNTfECTious MOSAIC DISEASE OP CUCUMBER. In Phytopathology, 

 V. 6, no. 2, p. 145-147. 



(3) Giissow, H. T. 



1918. OBSERVATIONS OxX OBSCURE POTATO TROUBLES. In Phytopathology, v. 



8, no. 9, p. 491-495' ^g- 2-5- 



(4) Johnson, G. W. 



1847. THE POTATO. ITS CULTURE, USES, and history. i8ip.,front. London. 

 Reprinted from Gard. Monthly, v. i. 



(5) McClintock, J. A., and Smith, L. B. 



1918. TRUE nature op SPINACH-BLIGHT AND THE RELATION OP INSECTS TO ITS 



TRANSMISSION. In JouT. Agr. Research, v. 14, no. i, p. 1-60, i fig., 

 pi. A, i-ii. 



(6) Melchers, L. E: 



1913. the mosaic disease of the tomato and related plants. in ohio 

 Nat., V. 13, p. 149-173. I fig-, pl- 7-8. Bibliography, p. 169-173. 

 Reprinted as Contrib. Bot. Lab. Ohio Univ., no. 74. 



