74 Journal of Agricultural Research voi. xxii. no. 2 



the absence of any aeration was the cause of this abnormal type of rot- 

 ting, and the following method was devised to allow for aeration. 



The principle j[inally decided upon was that of passing a current of 

 air, kept at a constant pressure, through sulphuric-acid towers and then 

 over calcium chlorid and sodium hydrate. This gave a constant stream 

 of dry, sterile air. The air was then passed over sterile water to bring 

 it to a desired humidity. The amount of water necessary for a given 

 humidity was determined by trials, and the air was then passed into the 

 jars containing the tubers. An outlet was provided at the bottom of 

 the jar. These jars were connected separately with the current of air 

 and not in series. Relative humidities were obtained and used through- 

 out the experiment as follows: i, 30, 70, and 100 per cent. These rela- 

 tive humidities were used at three different temperatures — 9°, 12.5°, 

 and 25° C. The set at 25° was placed in an incubator in the laboratory, 

 the set at 12.5° was placed in a special low temperature incubator, and 

 the set at 9° was placed in a well-insulated ice box. Each of these 

 temperatures was maintained within a variation of 2° throughout the 

 experiment. In this way four gradations of humidity at each of three 

 temperatures were obtained. The method provided the tubers with suf- 

 ficient aeration and secured sterile conditions throughout the experiment, 

 since the jars containing the tubers were not moved or opened until the 

 end of the period. 



The humidity readings were taken by the wet- and dry-bulb method, 

 the thermometers being inserted into the stream of air at the entrance 

 to the jar. The readings were found to vary, and at least 10 trial read- 

 ings were taken for each jar after the preliminary determinations were 

 made and the apparatus was set up. These readings ranged as follows : 

 I to 10 per cent, 20 to 40 per cent, 60 to 80 per cent, and 90 to loo per 

 cent. These were the greatest extremes found; and since a knowledge 

 of the approximate relative humidity is all that is necessary in an experi- 

 ment of this kind, these readings were taken to be sufficient, inasmuch 

 as they showed a gradual gradation from approximate dryness to satura- 

 tion. The ranges given above simply denote the possible error due to 

 the method of taking the readings. The humidity necessarily remained 

 constant, since the temperature, water surface, and air pressure were 

 constant. It was found to be impossible to use the wet- and dry-bulb 

 method to determine the relative humidity at the lower temperatures. 

 The changes of temperature caused by opening the door to make the deter- 

 minations were found to change the readings. Therefore the sets at 9° 

 and 12.5° C. were installed temporarily at 25°, the preliminary deter- 

 minations were made, and the readings were taken at that temperature 

 and corrections made by the use of psychometric tables (13). 



The large battery jars were fitted with wire screen supports, and six 

 tubers were used in each jar — four inoculated and two controls. The 



