GROWTH OF ENDOTHIA PARASITICA 
Such temperature indices must take into consideration both the daily 
temperature means and the frequency with which those means occur 
during the period under consideration. 
Among the methods suggested for attaining this desired end the 
one most widely used has recently been designated by Livingston (3) 
as a summation of remainder indices. This method consists in sub- 
tracting a certain assumed minimum from each daily mean tempera- 
ture and summing the remainders. A second^ method was suggested 
a few years ago by the Livingstons (2). It is based on the supposition 
that plant growth follows the chemical principle of van't Hoff and 
Arrhenius, which states that the velocity of many chemical reactions 
approximately doubles with each increase in temperature of 10° C. 
On this basis these authors have computed efficiency indices for the 
various temperatures, using 40° F. as unity. 
The two methods just described are open to the theoretical objec- 
tion that they fail to take into account the fact that the highest tem- 
peratures experienced in nature do not permit as rapid growth as 
somewhat lower temperatures. 
In an attempt to overcome this defect Livingston (3) has recently 
published a series of temperature efficiency indices based on actual 
physiological experiment. Using the data obtained by Lehenbauer 
(i) for the average hourly rates of elongation of shoots of seedling 
maize plants when exposed for periods of twelve hours to temperatures 
of 12 to 43° C, he has derived a series of indices which express the 
average hourly growth rate for each degree C. or F. in terms of the 
growth rate for 4.5° C. (38° F.) considered as unity. 
This series differs from the two described above in that the indices 
gradually increase up to a certain point (89° F.) and then decrease at 
higher temperatures. The optimum temperature thus indicated is of 
course that of the maize seedling under the conditions of Lehenbauer's 
experiment and is higher than any daily mean reached during this 
investigation. Moreover, the rate of increase in index value between 
the minimum and optimum for growth is much more rapid in the 
physiological series than in either of the other series. So far as the 
present study is concerned this constitutes the chief difference between 
this system and the other two. 
3 These methods of interpreting temperature data are rather fully discussed by 
Livingston (2 and 3) and their application to the study of Endothia parasitica by 
the writer (4). 
