INFLUENCE OF CERTAIN CLIMATIC FACTORS 
13 
a much longer frost-free period than Amherst, Mass., while the amount 
of growth at these points is practically the same. The curves, figure 2, 
in which the length of frost-free period at the various points is indi- 
cated in percentage of the period at Charlottesville, show that while 
there is in general a falling off in the length of frost-free period from 
Charlottesville to Concord, the agreement between this curve and the 
curve of growth is not such as to indicate any direct causal relation. 
Table V 
Frost Data for Various Localities 
Locality 
Concord, N. H 
Amherst, Mass 
Williamstown, Mass. 
Hartford, Conn 
Mohonk Lake, N. Y, 
Wilmington, Del. . . . 
Van Bibber, Md 
Woodstock, Md 
Frederick, Md 
Washington, D. C. . . 
Charlottesville, Va. . . 
First Killing Frost 
in Autumn, 1914 
Last Killing Frost 
in Spring, 1915 
Length of Frost-free 
Period in Days 
October 
September 29 
28 
29 
27 
14 
28 
September 29 
29 
October 28 
28 
28 
May 15 
20 
April 22 
13 
14 
4 
15 
15 
15 
3 
5 
137 
131 
160 
197 
183 
207 
167 
167 
196 
208 
206 
Temperature 
In measuring the effectiveness of temperature in plant climatological 
studies annual or monthly means are obviously of very little signif- 
icance. As has been frequently pointed out, localities with similar 
mean annual temperatures may have actually very different climatic 
conditions. Among the methods of measuring temperature more 
satisfactorily probably the most used is that of direct summation of 
daily mean temperatures. Merriam (6) was the first to apply this 
method in preparing a chart of the climatic zones of the United States. 
Briefly, the method is as follows: A certain minimum temperature is 
assumed as a starting point and the amount added to the summation 
each day is the number of degrees above the assumed minimum which 
represents the mean temperature for that day. The minimum is 
sometimes the freezing point but often a somewhat higher temperature. 
Recently the Livingstons (5, p. 353) have called attention to the 
act that although these temperature summations have in many 
nstances furnished data consistent among themselves and constituting 
an apparently reliable criterion for the measurement of the intensity 
