Aug. 2i, 1916 Control of Powdery Dryrot of Potatoes 825 



then closed, wrapped, and stored. Eight of these samples were obtained : 

 Two of Netted Gem and one of Idaho Rural from desert land plots, 

 and one of the Netted Gem and two of Idaho Rural from alfalfa-land 

 plots. The remaining two samples were taken from the check plots 

 which were planted on alfalfa land. One was a sample of the Netted 

 Gem variety, and the other was an Idaho Rural. Two months after 

 storing the samples, the boxes were opened and the tubers examined. 

 Every tuber in each of the eight boxes showed at least slight signs of 

 decay, and some showed deep infection pockets of dryrot. 



Isolations were made from the decayed portions of the tubers and the 

 presence of the organism determined. Not a single culture gave nega- 

 tive results. It is apparent, therefore, that F. trichothecioides is at the 

 present time well distributed in desert soils, as well as in those previously 

 in cultivation, and is not necessarily introduced on the seed. 



RELATIONSHIP OF TEMPERATURE TO THE DEVELOPMENT OF 

 POWDERY DRYROT 



The experiments to determine the relationship of temperature to the 

 development of powdery dryrot were carried on in the laboratories in 

 Washington and in the cold-storage rooms of a Washington cold-storage 

 plant. In these experiments potatoes of the following varieties were 

 used : Idaho Rural, Netted Gem, Peoples, Pearl, Burbank, and Improved 

 Peachblow. Three different experiments were undertaken. 



1. Tubers of each of the above varieties were first washed and disin- 

 fected by fumigating with formaldehyde gas. Two methods of inocula- 

 tion were employed. The first method consisted in cutting off the stem 

 end of the tuber and dipping the cut surface into a spore suspension of 

 F. trichothecioides. The second method consisted in inoculating the 

 tubers by puncturing the skin with a needle inoculated with the spores 

 of the fungus. In both cases the inoculated tubers were wrapped 

 separately in sterile paper. Tubers inoculated by each of these methods 

 were placed in the incubators and in the incubator room. Checks were 

 prepared in the same manner except that the tubers in one case were 

 dipped in sterile water and in the other case were punctured with a sterile 

 needle. 



2. In the second experiment sterile blocks were cut from tubers from 

 each of the varieties named. These sterile blocks were placed in sterile 

 culture tubes and allowed to incubate for several days in order to insure 

 their sterility, after which they were inoculated with the fungus and 

 placed in the incubators and in the incubator room. 



3. In the third experiment half -bushel lots of each of the varieties 

 above named were first washed and disinfected by fumigating with for- 

 maldehyde gas. Each tuber was then cut across the stem end and the 

 cut surface dipped in a spore suspension of the fungus, after which they 



