5o8 Summary of Agricultural .Expfriments. [sept., 



Potato "Leaf-Blotch" and "Leaf-Roll" (Jour. Roy. Hort. Soc, 

 Vol. 36, Pt. III., May, 191 1). — In 1908-10 Mr. A. S. Home found 

 in Scotland three outbreaks of a leaf-blotch disease, all of which 

 appeared in crops raised from seed potatoes of the President variety 

 brought from the Continent. The blotches had a dark brown centre, 

 surrounded by a margin of a lighter shade, and in the examples 

 examined, which were all of a late stage of the disease, it worked its 

 way from the surface of the leaves into the more deeply seated tissue. 

 This is in contrast to the ordinary leaf-curl disease, due to Macro- 

 sporium solani, in which the fungus reaches the leaves last. The 

 diseased plants were stunted, with yellowish foliage and blotched leaves, 

 sometimes half-folded or curled, and, when lifted, the tubers were few 

 and very small. From this crop tubers of large size, and therefore 

 from apparently healthy plants, were chosen and planted, but the disease 

 was quite as bad, while when the small ones were used practically no 

 crop was obtained. 



A number of plants with curled or rolled leaves were also observed 

 by Mr. Home in Durham, and, on lifting, were found to be affected 

 with Blackleg. 



Potato Blight (Phytophthora infestans) (Scientific Proc. Roy. Dublin 

 Soc, Vol. XIII., No. 2, March, 1911)- — Considerable uncertainty exists 

 as to the manner in which potato plants first become infected with 

 Phytophthora infestans in each succeeding season, and in the absence 

 of resting spores, capable of living over the winter, it has been sup- 

 posed that diseased tubers containing the mycelium must be the source 

 from which the blight starts anew in any given season. These experi- 

 ments were carried out to ascertain whether the plants become infected 

 in the field directly from the planted tubers by means of mycelium and 

 not by spores. 



Six potato tubers infected with Phytophthora and six healthy 

 tubers were halved, tnus making twenty-four sets. These were planted 

 in pots, of twelve of which the soil had previously been sterilised. The 

 soil in each case was virgin loam not previously used for potting, and 

 no manure was used. Three pots containing diseased sets in sterilised 

 soil were placed under conditions extremely favourable to the develop- 

 ment of Phytophthora, three pots containing healthy sets in sterilised 

 soil being used as controls. Two of the diseased sets produced plants 

 absolutely free from Phytophthora, while the third rotted away in the 

 soil. 



The remaining eighteen sets were placed under conditions less favour- 

 able to the growth of the fungus. Of the nine diseased sets, six pro- 

 duced plants, one of which was infected with Phytophthora and re- 

 moved. Subsequently eight of the nine healthy plants which had been 

 produced from the nine healthy sets, and four of the plants from the 

 diseased sets, became infected with the blight, it being practically 

 certain that infection was brought about by the spores set free from 

 the diseased plant before its removal. The two remaining plants, one 

 from a healthy set and one from a diseased set, were kept for some time 

 longer under conditions favourable to the blight, but did not become 

 infected. 



A further experiment was carried out during the summer of 19 10 

 in Co. Galway. Of 132 uncut tubers attacked by Phytophthora planted 



