15 



approximately proportional results for ordinary growing tem- 

 peratures. This fact has been noted by Livingston and 

 Livingston and again by Stevens and it Is also obvious from 



f 



Stevens, Ileil 3., Influence of t emperature on the growth 



of Endothia Parasitica. Am. Jour. Bot. 1: 2, 112-118.1917 

 Idem, Influence of certain climatic faotO'S on the develoo- 

 ment of Endothia parasitica. Ibid. 4:1, 1-33.1917. 



the climatic data given by ITcLean. 



A third method of expressing temr)erature ae ' -^ effects 

 plant growth has been more recently suggested by Livingston . 

 From the results of Lehenbauer's experiments on maize seedlings. 



^ 



V Livingston, B. E. , Physiological temperature Indices for 

 the study of pXant growth in relation to climatic conditions. 

 Physiol. Res. 1^: 8, 399-420.1915. 



V Lehenbauer, P. A., Growth of maize seedlings in relation 

 to temperature. Phyfeiol. Res. I ;247-288.1914. 



Livingston derived a series of coefficients giving the effi- 

 ciencies of various temperatures in terms of the growth of 

 this plant.. He has called these "physiological temperature 

 indices". The growth rates upon which the index values are 

 based are those shown by the seedlings when exposed for 12 

 hours to a maintained temperature, the other conditions of 

 the ex-^eriment being approximately the same for all experi- 

 ments. It is suggested that t e coefficients thus derived 



