Sept. IS, 1919 Temperature in Relation to Quality of Sweetcorn 281 



factory basis for estimating the temperature value for physiological 

 processes of a given climate has long been recognized, and the three sets 

 of indices represent three suggested methods of deriving from mean 

 temperatures some index which would more nearly represent temperature 

 efficiency. 



Remainder indices, derived by subtracting a constant quantity (in 

 this case 39) from each daily mean temperature, have been in use for 

 a considerable time. The other methods were suggested recently by 

 Livingston (7, 8), and all three are fully discussed by him in the papers 

 cited.* 



The exponential system is based on the supposition that plant growth 

 rates follow the chemical principle of van't Hoff and Arrhenius, which 

 states that the velocities of chemical reactions about double with each 

 increase in temperature of 10° C. The physiological indices were cal- 

 culated from actual temperature values for the growth of corn (maize) 

 seedlings from 10 to 12 mm. high, as worked out by Lehenbauer (6). In 

 view of Appleman and Arthur's conclusion (2) that the average tempera- 

 ture coefficient of sugar depletion in sweetcorn is about 2, Livingston's 

 "Exponential Indices" based on a coefficient of 2 are of special interest. 



The degree of accuracy with which any index derived from mean 

 daily temperatures — }4 (maximum -{-minimum) — expresses the tempera- 

 ture of the day must depend somewhat on the daily temperature range 

 and on the shape of the curve of hourly temperatures. In figure i are 

 plotted the curves of normal hourly temperatures for August at Balti- 

 more, as published by Fassig (5, p. 61), and the mean hourly tempera- 

 ture at Portland for September, 1918.' It will be obseived that the 

 curves are of the same general shape and that the daily ranges of tempera- 

 ture are similar. 



The curves of mean hourly temperatures shown in figure i furnish a 

 striking evidence of the difference in the temperatures of the contrasted 

 regions during the corn-packing season. The highest mean temperature 

 at Portland, 62.6° F., is 6° below the lowest mean temperature for 

 Baltimore, 68.6°. 



From the purposes of the present paper, however, it is unimportant to 

 determine which method most nearly represents the actual rate of loss, 

 since on whatever basis the comparison is made it is evident that the 

 average day during the corn-packing season in Maryland is much warmer 

 and therefore much more severe in its effect on sweetcorn than the 

 average day of the corresponding season in Maine. Deterioration of 

 corn after picking during a given period would then ordinarily be much 



' These three kinds of temperature efficiency indices have been compared by one of the writers in con- 

 nection with studies of the growth of fungi in relation to temperature (i^). 



2 Thenormalhourly temperature for Portland has not been computed. The curve for Portland was pre- 

 pared from data for the month of September, 1918, kindly furnished the writer by Jlr. Edward P. Jones, 

 Meteorologist, in charge of the Portland. Me.. Station. This, according to advice from Dr. P. C. Day, Chief 

 of Climatological Divisiou, of the U. S. Weather Bureau, gives a fairly representative curve. 



