1148 



Immunity Trials of Potatoes, 1921. 



[Mar., 



it soon became apparent that the varieties of potatoes would 

 behave in a most abnormal manner. Varieties usually pro- 

 ducing kidney-shaped potatoes tended to give ovals instead, 

 while the oval varieties tended to yield rounds; the plants 

 produced much secondary growth of the haulms ; the first- 

 formed tubers, even when quite small, sent out sprouts of 

 considerable length. All the peculiarities due to the abnormal 

 conditions had to be sifted out by Mr. Bryan before any true 

 characteristics of the varieties could be determined and re- 

 corded, and for this work great ingenuity aud patience were 

 required on the part of the recorder. The main object of the 

 trials was to provide a test from the results of which the 

 Ministry would be able to decide as to the further varieties to 

 be added to the list of Approved Immune Varieties for the 

 purpose of the Wart Disease of Potatoes Order of 1919. It 

 will be remembered that varieties are not added to the list 

 until the Ministry is satisfied that they have successfully under- 

 gone a thorough test conducted on scientific lines. Generally 

 one year's test must be considered insufficient for the results 

 to be interpreted with accuracy; and decisions are given after 

 the varieties have successfully passed through two consecutive 

 tests, provided the weather during these years is normal in 

 character. 



The trials in 1921 were affected by the abnormal weather 

 conditions to such an extent that, save in the case of a few 

 varieties, no dependable interpretation of the results could be 

 made, and the tests for most varieties will therefore need to 

 be repeated in 1922. The Ministry regrets the unavoidable in- 

 convenience that this may cause to breeders and raisers; but 

 experiments in past years have definitely shown that the 

 intensity of the disease is largely influenced by the amount of 

 rainfall, and as this was but 6 inches during the months of 

 June, July, and August, one would not expect to find much 

 disease on any of the susceptible varieties, so that its absence 

 could not be taken as proof of immunity. 



The arrangement of the trials adopted in previous years was 

 slightly modified, the different sections of the trials being- 

 arranged in proper groups. In the Immunity Trials there were 

 782 plots, of which 96 were being tested for the second time 

 and 686 were being tested for the first time. Amongst those 

 being tested for the second time, w T art disease appeared late in 

 the season in 9 varieties (Eestorator, Ben Venue, Ben Lawers, 

 G-odolphin, Geante Sans Pareille, Seedling B.5, Seedling B.6, 



