Wire Stem of Cabbage 



22° and 26° C. (table 2). The figures given in the table represent the 

 averages of three trials. 



The pH range for growth 



The relation of the growth of the fungus to the hydrogen-ion concen- 

 tration in culture was determined by making transfers from a young 

 culture to petri dishes containing a freshly made medium adjusted to the 

 desired acidity or alkalinity, and measuring the diameter of the area 

 covered after five days of growth. Exactly 200 cubic centimeters of 

 freshly prepared potato agar was placed in flasks. The proper number 

 of drops of M/5 HC1 or M/5 NaOH to produce the desired pH in each 

 flask, as determined roughly by a preliminary trial, were placed in test 

 tubes plugged with cotton. One tube was prepared for each flask. Where 

 only a few drops were to be added to the medium, about 5 cubic centi- 

 meters of distilled water was placed in the tube to facilitate the delivery of 

 the reagent from the tube to the flask. Several tubes containing 10 drops 

 of either the acid or the alkali were also prepared as reserve tubes. In 

 case the original amounts of reagent added did not produce the desired 

 hydrogen-ion concentration, these known amounts were added to the 

 partially adjusted media while it was still warm, without unnecessary 

 delay or reheating. Both flasks and tubes were autoclaved for fifteen 

 minutes at 15 pounds pressure. Without being permitted to solidify, 

 the medium of each flask was adjusted by pouring into it the reagent from 

 the corresponding tube and the pH was determined. In other trials, 

 in which it was impossible to complete the adjustment for lack of time, 

 the medium was not adjusted at the time of sterilization, but was allowed 

 to cool and was reheated when the entire operation could be completed. 

 The purpose of this was to eliminate complications which would result 

 from intervening cooling and heating. The pH determination was made 

 colorimetrically, with buffer mixtures, 9 and with the aid of a comparator 

 block. 10 Several samples of 5 cubic centimeters each were poured (not 

 pipetted) into test tubes, allowed to cool, and compared with the standard 



• Clark, W. Mansfield. The determination of hydrogen ions, p. 1-317. 1920. 



10 Gillespie, Louis. Colorimetric determination of titration curves without buffer mixtures. Amer. 

 Chem. Soc. Journ. 42:742-748. 1920. Also, Colorimetric determination of hydrogen-ion concentration 

 without buffer mixtures, with especial reference to soils. Soil sci. 9:115-136. 1920. 



