Mar.i,i 9 « Temperature Efficiency for Ripening of Sweetcorn 801 



summations, were the first to apply velocity coefficients to the study of 

 effective climatic temperature conditions for plant growth. Upon the 

 basic assumption that the growth rate is unity at 40 F. and that it 

 doubles for each rise of io° C. (18 F.), they deduced temperature 

 efficiency values corresponding to temperatures, in whole numbers, from 

 40 to 99 F. These efficiency values are spoken of as exponential 

 indices. Since the rate of the carbohydrate changes in corn after it is 

 pulled has a temperature coefficient of about 2 for a range of tempera- 

 ture beyond the limits of the climatic temperature for either ripening 

 period, and since the chief process during ripening is the conversion of 

 sugar into starch, the exponential indices would be expected to furnish 

 the best criteria of the temperature efficiency for the ripening processes 

 in sweetcorn. In Table III are given the sums of the exponential indices 

 corresponding to the daily mean temperatures of each ripening period 

 under consideration, as well as the average daily index for each period. 

 The average daily index for the early season is 2.5 times greater than 

 that of the late season. If these indices furnish an approximate criterion 

 of the temperature efficiency for ripening of sweetcorn, the ripening 

 should have proceeded 2.5 times faster during the early ripening period 

 than during the late ripening period. The experimental data show that 

 this was actually the case; the late season required 15 days to carry 

 the corn to the same stage of ripening that required only 6 days in the 

 early season, a time ratio of 2.5. 



More recently Livingston l has derived a new set of temperature 

 indices which he terms physiological indices, since they are based upon 

 Lehenbauer's actual measurements of the hourly rate of elongation of 

 the shoots of seedling maize plants. For the sake of comparison these 

 indices for the two ripening periods are also given in Table III, but it 

 will be seen at once that they do not furnish even an approximate cri- 

 terion of the temperature efficiency for the ripening processes in sweet- 

 corn. This may be at least partially explained by the fact that, for 

 the processes under consideration, the principle of Van't Hoff and 

 Arrhenius seems to hold for rather a wide range of temperature, while 

 in the elongation of maize shoots it holds only for a range of tempera- 

 ture from about 20 to 30 C. 



1 Livingston, Burton Edward, physiological temperature indices for the study of plant 

 growth in relation To climate conditions. In Physiol. Researches, v. i, no. 8, p. 399-420, 4 fig. 

 1916. Literature cited, p. 420. 



