1038 Summary of Agricultural Experiments, [march, 



mixture injured the tubers without preventing disease. It was, how- 

 ever, found possible to destroy the fungus on diseased tubers (without 

 seriously affecting the vitality of the tubers) by heating to 50 0 C. 



Attempts to discover the exact source of infection of tubers did not 

 yield conclusive results, though it seems probable that it is not due to a 

 preliminary contamination of the soil with resting spores from a previous 

 season. 



The Stalk or Sclerotium Disease. — It was concluded in 1910 that 

 plants are infected with this disease by air-borne spores, and not by 

 mycelium or spawn in or on the surface of the soil. This was confirmed 

 in 191 1, when some old grass land was broken up and planted with 

 potatoes. The soil was free from the disease, and yet very many of the 

 plants were affected by the stalk disease, infection doubtless taking place 

 from spores borne by the air from " spore-cups " present in abundance on 

 neighbouring land. 



The Stalk disease appeared to suffer no check from the dry season, 

 and about the end of July had made such progress that a couple of 

 nights of strong wind broke down the infected plants at the point of 

 infection. 



Various methods of treatment to prevent this disease were experi- 

 mented with, but were quite ineffective. A very striking result was, 

 however, obtained on a plot which was planted late (May 27th), as 

 compared with April 6th in the other plots. Only 5 per cent, of the 

 plants on this plot were attacked, as against from 95 per cent, to 100 

 per cent, on the others. The total yield of potatoes was, however, 

 somewhat seriously reduced. 



Black Stalk Rot and Corky Scab were much less prevalent than in 

 previous years, and it was impossible to obtain definite results, though 

 in the case of the Scab, application of Flowers of Sulphur at the 

 rate of 6% cwt. per acre appeared to be beneficial, as it not only reduced 

 the proportion of diseased tubers, but increased the total crop. Short 

 accounts are also given of "Leaf-curl" and "Leaf-roll," " Sprain," "A 

 new form of Tuber-Rot," and " Pitting Experiments." (A note on the 

 1910 investigations appeared in this Journal for August, 191 1, p. 419.) 



A Disease of Sweet Peas, Asters, and other Plants {Roy. Bot. Gard., 

 Kew, Bull. Misc. Inform., No. 1, 1912). — Mr. G. Massee describes the 

 minute parasitic fungus (Thielavia basicola, Zopf), and gives an account 

 of investigations carried out at Kew. In recent years the damage 

 done to asters and sweet peas has been so extensive in some localities 

 that their cultivation has had to be abandoned. Culinary peas and 

 many other plants may also be affected, while in Europe and the United 

 States tobacco has suffered to a serious extent. The symptoms vary 

 a little according to the extent to which the soil is infected, but gener- 

 ally the disease is only serious during the seedling stage. In the case 

 of peas, both the plumule and radicle may be attacked, and then the 

 seedlings will not appear above ground at all. More commonly, how- 

 ever, the root only is directly affected, in which case the plant attains 

 considerable growth, then suddenly wilts, turns yellow, and dies. Another 

 very common symptom is known to growers of sweet peas as "streak" 

 or "stripe," characterised by the presence of dingy yellow streaks on 

 the stem and leaves. In asters the plants are killed outright during 

 the seedling stage; when about 3 in. high they begin to wilt, and 



