16 



of this wash water were transferred to Petri dishes and a tube 

 of melted 3% dextrose agar (+10), which had been previously 

 cooled to 42-45 °C., added to each plate. The quantities of wash 

 water found the most satisfactory and used in nearly all 

 cases were 1 cc, 10 drops and 5 drops to each Petri dish^ al- 

 though in a few instances it was thought advisable to add to 

 these a greater dilution, and 1 cc. from a second flask (con- 

 taining 1 cc. of wash water in 100 cc.) was used. A record 

 was kept of the number of drops delivered by each pipette, and 

 this was found to be fairly constant for any single pipette, al- 

 though it varied considerably for the different ones used. 



The plates were incubated in the laboratory, the temperature 

 of which was kept approximately at 25° C. Colonies suspected 

 of being the blight fungus were marked on the fourth day with 

 India ink, and the counts were verified two or three days later, 

 at which time any doubtful colonies were transferred to agar 

 slants to make certain of their identity. A count was also 

 made of the number of bacterial or yeast colonies, the number 

 of fungous colonies not Endothia parasitica^ and the number of 

 species of fungi represented other than the blight fungus, as 

 nearly as could be determined from cultural characteristics. 

 Knowing the calibration of the pipette used, it was an easy 

 matter to compute from the above information the number 

 of viable spores of the blight fungus, the number of spores 

 of other fungi and the number of bacteria and yeasts carried 

 by each insect. 



Those insects which had been used in the laboratory and 

 insectary tests were collected and cultures made from them in 

 essentially the same way as those brought in from the field, 

 except that no record was kept of the number of fungous species 

 represented in the cultures. 



After the plates had been poured, the insects were preserved 

 for classification, and beginning with insect No. 34, a few cc. 

 of formalin were added to the wash water to inhibit the growth 

 of spores. At a later time the wash water from those insects 

 yielding positive results was centrifuged in 10 cc. quantities 

 and the sediments thus obtained thrown together and centri- 

 fuged again. All but a small quantity of water at the bottom 



