950 



The Distribution of Wart Disease. 



[Jan., 



On clean land neither of these varieties would prove superior 

 croppers to the susceptible kinds. The great loss of crop 

 which must be attributed to the ravages of Wart Disease is a 

 serious matter to the farmer. 



Conditions influencing Intensity of Disease. — For several 

 years there has been a general belief that the intensity of the 

 disease was greatly increased during periods of excessive rain- 

 fall, but until 1919 no actual figures were available to confirm 

 this belief. Previously, many of the highly susceptible varieties 

 produced crops of warted tubers far in excess of the clean crop, 

 but in 1919 the intensity of the disease was so slight that in all 

 cases the reverse held good. In view of the fact that there was 

 no rain in 1919 from mid-April until the 29th June, and, in fact, 

 very little during the summer, it appears highly probable that the 

 lack of moisture was the essential factor lessening the intensity 

 of attack. 



The following figures taken from Mr. Snell's report illustrate 

 this point : — 



; Clean Tubers. Warted Tubers. 



Variety. 



Tons. 



Cwt. 



Tons. 



Cwt. 



1918 Cumberland Ideal 



1 



11 



3 



18 



1919 



1 



13 





19 



1918 Arran Chief ... 



2 



5 



. , 5 



12 



1919 „ „ 



5 







15 



1917 General 



4 



15 



4 



19 



1919 „ 



3 



5 



4 



11 



Where a variety usually gave a greater proportion of clean 

 tubers than warted, the weight of the latter was much less than in 

 previous years. 



Clean Tubers. Warted Tubers. 



Year. Variety. Tons. Cwt. Tons. Cwt. 



1918 Epicure 6 15 1 12 



1919 „ 3 17 — 3 



1919 „ 3 16 — 1 



A point of considerable scientific interest, and one which 

 Mr. Snell had hoped to investigate, is that the proportion of 

 clean to warted tubers varies considerably with the variety. 

 This conclusion has been arrived at after four years' work, and 

 in 1919 it was hoped to travel further along this line of investiga- 

 tion, but the dry season rendered all observations almost worth- 

 less. In order to illustrate the point, a table of figures 

 obtained in 1918, of varieties of certain types, with the weights 

 of clean and warted tubers is given : — 



