Sept. IS, 1919 Investigations on Mosaic Disease of the Irish Potato 269 



appeared to be very slightly mottled but questionable for mosaic in 191 7 

 were mottled and nonmottled plants noted in 191 8. Observations upon 

 the foliage symptoms were made at three different times during July 

 and August, the first observations being made when the vines were from 

 2 to 6 inches tall and the last just before the vines began to die. 



In connection with the observations on the behavior of the vines of 

 hill-selected stock, studies were made also on the effect of mosaic on 

 yield. The hills were selected from some of the same stock on which 

 notes upon the performance of the foliage were taken, and hence the 

 stages of the disease indicated here answer the same description as those 

 presented in connection with the notes upon the behavior of the foliage 

 as indicated in Table VIII. Table IX gives the effect on yield of these 

 hill selections. 



Tablu IX. 



-Hill selections: Effect of mosaic of potato on yield in laboratory plots, 

 Presqtie hie, Me., igiy-iS 



Plot 



No. 



4 

 4 

 4 

 4 

 4 

 5 

 5 

 5 

 5 

 5 

 5 



16 

 16 

 16 

 25 



25 



25 

 25 

 25 

 36 

 36 

 36 

 37 

 37 

 37 

 37 

 37 

 37 

 37 

 37 

 37 

 37 

 37 



Condition of stock in 1917 

 and 1918. 



Healthy 



....do. 



....do.. 



. . . .do. . 



....do.. 



....do.. 



....do.. 



....do.. 



....do.. 



....do.. 



....do.. 



Slight... 



....do.. 



....do.. 



Bad . . . 



....do.. 



...do.. 

 ...do.. 

 ....do.. 

 Medium 

 ...do.. 



...do.. 

 ....do.. 

 ....do.. 

 ....do.. 

 ....do.. 

 ....do.. 

 ....do.. 

 ....do.. 

 ....do.. 

 ....do.. 

 ....do.. 

 ....do.. 



Hill 

 unit. 



4A 

 4C 

 4D 

 4K 



4F 

 5A 

 5B 

 5C 

 5D 

 5E 

 5F 



I6R 

 I6H 

 I6I 



2SA 



2sE 

 25F 

 25H 



2SJ 



36A 



36B 



36C 



37A 



37B 



37C 



37D 



37E 



37F 



37G 



37H 



37I 



37J 



37K 



Num- 

 ber of 

 hills. 



Total 

 yaeld. 



15 



II 



6 



3 



3 

 5 



7 



14 



Average 



yield 

 per hill. 



Lb. Oz. 



I 15 



I 14 



1 14 



2 5 



1 14 



I 12 



I 15 



I 12 



1 14 



2 A 

 2 \\ 

 I 10 



I 4 



I 3 



4 



8 



5 



7 



5 



I 13 



2 y2 



3 



13 



6 



Yield of 

 parent 

 hill in 



1917. 



Oz. 



5 



13 

 9 

 9 



14 

 9 

 6 

 6 

 4 

 14 

 12 



Yield per hill in 



1918 compared 



with that of 191 7. 



