6o8 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



Some of these diseased tubers were exhibited and reported upon 

 before the Scientific Committee of the Royal Horticultural Society 

 in 1912.* 



Owing to various circumstances these experiments could not be 

 repeated in the following year. 



The results obtained from the experiments in Scotland suggested 

 the possible infection of the crop by an organism or organisms. Now 

 I have already pointed out that blotch and streak are not caused by 

 a fungal organism ; if one is present at all, it would probably be of 

 bacterial nature. Should this prove to be the case, we are faced 

 with the possible infection of crops not only through planting diseased 

 tubers but through planting healthy tubers raised on infected land 

 and carrying infected soil. 



During the period covered by these investigations the Director 

 had from time to time received specimens of diseased tubers sent from 

 different parts of the country, and several cases were reported to him 

 at the Laboratory in 1911, 1912, and 1913. He accordingly agreed 

 that it was advisable to conduct some experiments at Wisley, and 

 amongst other things suggested trying the effect of planting tubers 

 washed in tap-water to remove adherent soil, and not washed, with 

 the object of testing the point at issue. 



Experiments, 191 2. 



Exp. I. An experiment was designed with the object of attempting 

 to infect disease-free tubers, planted at Wisley in soil not previously 

 used for potatos, with streak. 



The potatos used were ' Duke of York,' kindly given by Messrs. 

 Sutton, who made a special effort to supply them from land which 

 had not produced crops affected with blotch or streak. I examined 

 the tubers when they arrived and found them free from disease- 

 An attempt was to be made to infect them by mixing supposedly 

 infected soil with the soil in which they were to be planted. The 

 imported soil was sent from the farm in East Lothian that had 

 produced the diseased 1 Duke of York ' potatos in the experiments 

 in 191 1. Unfortunately the soil was detained in Scotland during 

 the great railway strike, and arrived too late for the purpose of the 

 experiments. 



Exp. II. Experiment to determine the effect of washing tubers 

 obtained from a supposedly infected soil. 



The experiment was arranged as shown in Table I. The tubers 

 used were all ' Duke of York,' and lots A, B, C, and D were 

 chosen from those raised in the experiment carried out in Scotland 

 in the previous year. All the sets planted in lots A and C were 

 affected with streak, and all the sets in lots B and D were completely 

 free from streak, when planted. The tubers were tested by cutting 

 * See Journal R.H.S. vol. xxxvii.(i9i2) p. ccxix. 



