DEPARTMENT OF BOTANICAL RESEARCH. 61 



was accompanied by cessation of growth and was soon followed by 

 wilting. If waiting was not allowed to go too far the plants could be 

 revived by renewing the access of oxygen to the soil. The injurious 

 response was rapid and the revival slow. This study will be continued. 

 It has a number of important relations to both theoretical and practical 

 problems of the relations of plants to the soil solution. 



Physiological Indices of Temperature Efficiency for Plant Growth, 

 by B. E. Livingston. 



The interpretation of climatological temperature data with refer- 

 ence to plant growth has received still further attention during the 

 past year. Livingston and Livingston^ have summed the normal 

 daily mean temperatures above 39° F. for a large number of stations 

 in the United States, for the period of the average frostless season, and 

 have also sunamed, for the same period, the normal daily chemical 

 indices of temperature efficiency (supposing that chemical reactions 

 double in velocity with each temperature rise of 18° F.). They show 

 that the two charts of temperature efficiency values thus obtained, 

 tentatively representing the temperature influence for the entire period 

 of the average frostless season, are remarkably similar, but differ in 

 certain important details. Neither of these two methods of tempera- 

 ture efficiency summation has any direct physiological basis, and it is 

 obvious that neither method can be regarded as plausible for the higher 

 temperatures observed in nature; for both methods proceed on the 

 supposition that plant growth should continue indefinitely to increase 

 as the temperature rises, and this is well known to be in disagreement 

 with physiological observation. 



The publication of Lehenbauer's study of the relation between 

 temperature and the rate of growth of the shoots of maize seedlings^ 

 made possible a first attempt to derive phj^siological indices of tempera- 

 ture efficiency for plant growth. Lehenbauer's graph of observed 

 growth-rates for shoots of maize seedlings, for 12-hour exposures to 

 maintained temperatures, was conventionally smoothed, bj^ means of 

 a spline, and the ordinates of the smoothed graph were measured for 

 each whole degree Fahrenheit. The values thus obtained were then 

 expressed in terms of the value for 40° F., taken as unity, and these 

 numbers are tentatively regarded as indices of temperature efficiency 

 for plant growth. In making the summations for the climatological 

 study, each day in the period of the average frostless season is repre- 

 sented by the efficiency index corresponding to its normal mean tem- 

 perature and all of these indices for the period are summed for each 

 station considered. This method of summation has a theoretical 

 advantage over those heretofore tested, namely, that it takes account 

 of the existence of the physiological temperature optimum; the table 



iBot. Gaz., vol. 56. 349-375, 1913. ^phygioi. Res., vol. 1. 247-288, 1914. 



