134 



prisingly large aiiKiuiit of scab was noted. The soil, the treatment, and 

 the approximate percentage of scabbiness are given in Table I and photo- 

 graphs of the early' ijjota toes are shown in Figs. II, III, and IV. 



As the seed potato;,6^ had been treated it is evident that the scab spores 

 had lived over the winter in the pots which were left out in the ground. 

 It appears that very little scab bad snr^•ived the climate and soil condi 

 tions in the loam soil, while in the soils of more open texture such as 

 peat and sand, the spores bad been able to survive. 



The unfertilized soils in most cases are affected to the greatest extent. 

 In every case flowers of sulphur, which had been applied in 1912, has had 

 a deterrent eft'ect in the development of scab. In the fertilizer .treatment 

 sulphates have kept the scab down while the chloride has apparently en- 

 couraged it. 



The variations noted in the amount of scab on the potatoes grown in 

 silica sand merit special attention, as in these pots all factors except soil 

 treatment have been eliminated and there ai"e four pots which have not 

 had chloride in any form either in the original sand (the soils all have 

 more or less chlorine naturally) or in any treatment. The sulphur factor 

 was more nearly controlled in these pots than in the soil pots as di-calcic 

 phosphate was used in 1913 in place of acid iibospbate. Acid ph(is]ibate 

 which contains more or less calcium sulphate w.ms used in all soil pi)ts 

 that were fertilized; it was also used the first season in Ibc silica sand 

 pots, and it was necessary that son>e suljihate should be added as a plant 

 food. The treatment of each pot and the amount of scab on the potatoes 

 grown in silica are shown in Table II. Fig. V is a photographic reproduc- 

 tion of all the potatoes grown in the silica pots in 1913. It will be noted 

 from the accompanying table and illustrations tliat snlplnir li;is bad a 

 marked influence in reducing scab, but that sulphates ha\-e not. On the 

 other hand, wherever chloride lias Ijeen added eillier with or without sul- 

 phates very much scab was always present. This seems to indicate that 

 chlorides are needed in the development of the scab fungus. The fact 

 that chlorides are present in (piite large amounts in soils, especially those 

 near tlu; sea coast, may accoinit for the fact that chlorides have not been 

 found to increase scab in experiments where such (>rfects were note<l.* 



•II. J. Wheeler and G. M. TikIot, I?u1. 4(1, l{. I. I'.xp. St:i.: .-ilso C. I-:. Sicme, I'Olli Ann. Hep. 

 Mau. Agr. Kxp. Su., lilOS. 



