134 



prisiiigly large aiiumiit of scab was uotetl. The soil, the treatment, ami 

 the approximate percentage of scabl)iness are given in Table I and jihoto- 

 graphs of the early potatoes are sliown in Figs. II, III. and IV. 



As the seed potatoes liad been treated it is evident that the seal) spores 

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

 It appears that ^•ery little scab had sunived 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 had been able to survive. 



The unfertilized soils in most cases are .-itiecti'd to the greatest extent. 

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

 a deterrent effect in the development of scab. In thi^ 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 mei-it special attention, as in these jiots all factors except soil 

 treatment lia\c been eliminated and tlieic are four jtots which have not 

 h;id chloride in any form either in the original sand (the soils all have 

 more or less chlorine naturally) or in any ti'eatnieiit. The sulphur factor 

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

 phosphate was used in 1W3 in i)lace of acid plidspbate. Acid i)liosphate 

 which contains more or less calcium sulphate was used in all soil pots 

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

 pots, and it was necessary that some snli)hate 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 photograi)hic ivproduc- 

 tion of all the potatoes grown in the silica pots in 1!»].'!. It will lie noted 

 from the aci-oiuiianying table and illustrations that siilphnr has had a 

 marked influence in reducing .scab, but that sulphates have not. On the 

 other hand. wlieri'Ver chloride has been .-i.lded eilbcr witli or without sul- 

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

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

 that chlorides are present in ijuite large ;nuouiits in soils, especially those 

 near the .sea coast, may account for the fact that chloridt's have not been 

 found to increase scab in experiments where such effects were noted.* 



• H. J. Wheeler and G. M. Tucker, Bui. 40, K. 1. Kxp. Sta.; also O. K. Stone, 2()th .\nii. Hop. 

 Ma!.-!. Agr. Exp. Sta., 1908. 



