326 
The Philippine Journal of Science 
1917 
with the same diameter and 5.3 times as old as loblolly pine. 
These figures would indicate that Podocarpiis imbricatus on 
Mount Banahao is growing under much less favorable conditions 
than these different species of pine in the United States. 
The moisture conditions on Mount Banahao would appear to 
be favorable throughout the year, as the humidity is constantly 
high and the soil is moist. 
Unfortunately we have no exact method of comparing the ef- 
fects of various climatic factors in different regions. A means 
of estimating the effect of temperature on growth in different 
localities has been suggested by Livingston and Livingston.® 
They assume that the rate of growth is unity at 40° F. and that 
it doubles for every rise of 10° C. In other words that the 
effect of temperature on grov/th follows the well-known van’t 
Hoff principle. If t is taken as the normal daily mean tempera- 
ture on the Fahrenheit scale and if u is the corresponding tem- 
perature efficiency for growth, then according to the assumption 
The indices obtained in this manner are called exponential 
indices. The time element is taken into account by adding 
together the efficiency indices for all of the days of the frostless 
season. The results are summation indices. Following this 
method, Livingston and Livingston have prepared a chart of 
the temperature efficiencies for the United States. Livingston ® 
has devised another series of indices, based on Lehenbauer’s 
work on the relation of temperature to the rate of growth of 
maize seedlings. 
In Table V are given the summation indices for the period of 
an average frostless season, according to both systems, for New 
York and South Carolina; also summation indices for a whole 
year for the top of Mount Banahao. The figures for New York 
Table V. — Summation indices of temperature efficiency for plant growth, 
according to the physiological and exponential systems, for New York, 
Sozith Carolina, and the top of Mount Banahao. 
f " ' ■ ■ 
New 
South 
Mount 
1 
York. 
Carolina. 
Banahao. 
5, 968 
447 
16, 007 
884 
6,016 
736 
! Exponential - 
1 
° Livingston, B. E., and Livingston, G. L., Temperature coefficients in 
plant geography and climatology, Bot. Gaz. 56 (1913) 349-375. 
' Livingston, B. E., Physiological temperature indices for the study of 
plant growth in relation to climatic conditions, Physiological Researches 1 
(1916) 399-420. 
