336 



Journal of Agricultural Research 



Vol. XIX, No. 7 



of the 4,466 hills to be mosaic. Although this stock was retarded in its 

 development by being frozen nearly to the ground on June 23, only i per 

 cent of the hills developed mosaic between July 30 and August 18. The 

 nature of the various 191 8 plots and the percentages of mosaic on the 

 same ground in 191 9 are given in Table VIII. 



Table VIII. — Nature of igi8 plots and percentage of mosaic hills in the parts of the igig 

 plot grown upon the same ground 



Sec- 

 tion 

 No. 



Variety. 



Green Mountain. 

 Bliss Triumph . . 

 Green Moimtain. 



....do 



do 



Roxbury Wilson. 

 Bliss Triumph . . 

 Green Mountain. 



do 



Irish Cobbler. . . . 



do 



do 



Miscellaneous. .. 

 do 



II per cent mosaic. . 

 :55 per cent mosaic. . 

 13 per cent mosaic. . 



45 per cent mosaic. . 



46 per cent mosaic. . 



10 per cent mosaic. . 

 100 per cent mosaic . 



do 



1 1 per cent mosaic . . 



No leafroU 



All leafroll . 



No leafroll 



Leafroll and mosaic. 



do 



Total 

 number 

 of hills. 



424 

 432 

 454 

 422 



375 

 281 



350 

 458 

 140 



143 

 105 

 169 

 140 



573 



Percent- 

 age of 

 mosaic 



hills from 

 seed 

 pieces. 



24 

 23 



22 

 26 

 18 

 23 

 23 

 22 

 28 

 "22 

 22 

 15 

 23 

 24 



It will be noted that there are few marked deviations from the per- 

 centage for the whole plot, which was 23 per cent. These consist of one 

 deviation upward and one downward for the ground occupied by two half- 

 mosaic plots (4 and 5) and of the same for two comparatively mosaic- 

 free plots (9 and 12) and therefore are without significance in regard to 

 soil-harboring of the disease. 



SUMMARY 



(i) Transmission of potato mosaic by means of tubers, grafting, 

 plant juice, and aphids was eflfected under various conditions, including 

 those essentially of the field with insects controlled. 



(2) Infection was obtained with intervarietal transfer of juice. 



(3) Transmission was attempted, but without success so far as could 

 be ascertained in the same season, by means of flea beetles, Colorado 

 potato beetles, the seed-cutting knife, and contact of seed pieces, of 

 roots, and of vines. 



(4) Preliminary observations indicate that infection does not result 

 from growth in soil that produced mosaic potato plants the previous 

 season. 



