232 



Bulletin 230. 



A point which we would call particular attention to, as indicated 

 by the table and the chart, is the small difference between the mean 

 temperature of the different plats during the twenty-four hours 

 over which the observation extends. Upon studying the tempera- 

 ture curves of the different plats for the same period it was observed 

 that the temperature of the two-inch plat runs considerably higher 

 and lower than that of the others. This wide variation of the 

 hourly temperatures and comparatively uniform temperatures for 

 the twenty-four hours, embracing a night and a day, between the 



Fig. 183. — Chart condensed from 20 weekly records during the growing season, 

 shounng the range of temperature in the soil at different depths by periods of two 

 hours beginning at 6 A. M., tvith averages. 



Solid line represents temperature at 6 inches. 



Dashed line represents temperature at 4 inches. 



Dotted line represents temperature at 2 inches. 



different plats points to the conclusion that the quality of the tuber 

 is not so much affected by the sum total of temperature units, 

 within reasonable limits, as it is by the hourly variation of tempera- 

 ture through the twenty-four-hour cycles during the growing 

 season. 



It will also be noted that the mean temperature of the air for 

 the twenty-four-hour periods is not greatly different from the mean 

 temperatures in the soil for the same period, though the hourly 

 variation is markedly different. 



