1920] DISEASES OF PLANTS. 655 



Inj,- tlie ahility of tlie blackleg organism to withstand low temperatures within 

 inflated tiibors. the autlior inoculated healthy, disinfected potato tubers with 

 cultures of a strain of Bacillus atroscpticus. The tubers were then placed in a 

 moist chamber and allowed to remain at room temperature for 48 hours, at 

 which time all showed a nuirkod rot at the point of inoculation. The potatoes 

 were then packed in ice and placed in a refrigerator, where they were kept at 

 0° C. during the entire experiment. The tubers were examined at frequent in- 

 tervals and later planted in sterilized soil in the greenhouse. After the tubers 

 had been on the ice for 168 hours, the plate cultures showed that the number and 

 activity of the bacteria had decreased considerably. At the end of 11 days there 

 was still s«me bacterial growth, but it was reduced to a minimum. Tubers were 

 planted and two germinated and sent up sprouts which attained a height of about 

 2 in., when they died down immediately with blackleg. 



The results of this experiment are believed to show that infected tubers which 

 remain buried in fields at digging time decay to such an extent that they are 

 unable to germinate, or if they do germinate, the sprouts are killed by the 

 organism. This is believed to explain why blackleg is never found in volunteer 

 plants in Maine. 



Studies were made of soil in oi-der to determine whether the organism would 

 persist, but of the strains obtained from the soil which had overwintered in the 

 field, Dot one was found capable of producing blackleg rot. An attempt was also 

 made to inoculate plants by a watering method. The watering treatment was 

 begun when the plants were about 4 in. high and continued each week for seven 

 successive weeks. This experiment was duplicated in 1917. The tubers of all 

 plants growing during the season were found free from rot at harvest time. The 

 author's experiments are considered to show that unless the seed piece is in- 

 fected at planting time there is little chance that the plants will contract the 

 disease, even though the causal organism is washed about the stem and root 

 system. 



The potato leaf hopper and the hopper burn, E. D. Ball {Phytopathology, 

 9 (1919), No. 7, pp. 291-293).— Severe burning of potato foliage in 1918 is re- 

 ported as extending from Montana and Kansas to New York and New Jersey. 

 The author's attention was called to the condition in Wisconsin, and an examina- 

 tion of plants disclosed the fact that the partly burned leaves had one or more 

 nymphs of the potato leaf hopper (Empoasca mali) on the under side, while 

 the younger leave.s, still green, showed no trace of them. 



The potato leaf hopper is said to fly to potato fields soon after the plants 

 appear, and to lay its eggs in the midribs or leaf stems of the partly grown 

 leaves. Cage experiments in which a large number of adult leaf hoppers were 

 placed on a half-grown plant produced a bad burning and rolling of the leaves 

 in three days. Early planted potatoes were found to be most seriously injured, 

 because the leaf hoppers were then flying in greatest abundance. Tho.se planted 

 a few weeks later, after most of the eggs had been deposited, were practically 

 free from injury until the second brood appeared late In July or August. 



The author considers hopper burn as a specific disease, caused by a single 

 .species of leaf hopper. Spraying with Bordeaux mixture is said to act as a 

 partial repellant of leaf hoppers, but the most effective treatment was obtained 

 by use of Blackleaf 40, not weaker than 1 : 800 with 5 parts of soap added to it. 



Nomenclature of the potato scab organism, H. H. McKinney (Phyto- 

 pathology, 9 (1919), No. 8, pp. 327-529).— Attention is called to the work of a 

 number of authors, showing that Actinomyces chromogcnus is not a definite spe- 

 cies but a group of organisms differing iu physiology and morphology. On this 

 13621°— 20 5 



