114 
NEIL E. STEVENS 
Comparison of the amount of growth at the various stations for 
the year ending in the spring of 191 6 with that in the same locaHties 
for the years ending in May and in August, 191 5, shows a general 
agreement, although the growth at Charlottesville was only 23 centi- 
meters for the year ending in April, 1 91 6, as against 25 centimeters 
for the year ending in April, 1915. 
Relation of Rainfall to Growth 
In considering the influence of rainfall on vegetation both the 
total amount of precipitation and its frequency must be taken into 
account. Tables II and III give the monthly totals and number of 
days with over .01 inch of rain for each month during the period under 
consideration, together with the totals of the; twelve calendar months 
most nearly coinciding with the period for which growth was actually 
measured. From these it is apparent that no causal relation exists 
between the amount or the frequency of rainfall and the rate of growth. 
For example, the total rainfall for the year was very nearly the same 
at Williamstown as at Charlottesville but the growth was fifty percent 
greater at the latter point. Even more significant is the fact that 
although the rainfall at Concord, Williamstown, and Mohonk Lake 
was much greater for the year ending in May, 191 6, than for the year 
ending in May, 191 5, a difference of about twenty inches at Mohonk 
Lake, there was no perceptible difference in the rate of lateral growth. 
A comparison of the number of days with rain and of the rainfall 
for the warmer months at the various stations also fails to show any 
relation between rainfall and rate of growth. 
Methods of Computing Temperature Efficiency 
No method of interpreting climatological temperature data with 
reference to the influence of temperature on plant growth has yet been 
devised. The monthly and annual mean temperatures given in the 
climatological reports are obviously of little use for this purpose. 
Length of frostless season is of course important for many plants but 
has little or no significance for a fungus like Endothia parasitica, whose 
growth is by no means confined to the frostless season. In order that the 
temperature data given in meteorological reports may be really useful 
in plant climatology, it is necessary to obtain some kind of temperature 
indices which will express the effect of temperatures on plant growth. 
