7 
1922] HARVEY—PINE FORMATION 29 
Climatic factors 
The climatic conditions of the region in all probability are 
fairly revealed in the data taken at Luther (table I), less than ten 
miles to the southeast, at a United States Volunteer Station. It 
will be noted that the maximum range in temperature for the four 
years 1s 136°, from roo® in August 1918 to — 36° in February 1918. 
The average yearly rainfall for the four years is 33.65 inches, 
ranging from 28.29 inches in 1917 to 39.08 in 1920. The last 
killing frost in spring was.on June 23, 1920, and the first killing 
. TABLE I 
CLIMATIC FACTORS 1917-1920* 
Factors Jan. | Feb. | Mar.| Apr. | May | June | July | Aug. | Sept.| Oct. | Nov.! Dec. 
Mean maximum temperature 2 126.4 |42 56.1 |66 EER ey 7 54 43.7 130.8 
Mean minimum ture} 8.45) 7-7 |21.0 |30.7 |40.7 [52.0 [55.1 153.5 |46.2 139.6 |28.9 |16.8 
Maximum temperature. .... 5 Si Sh wey BS 
Minimum temperature..... —27 |—36 |—18 Ir 22 27 33 34 27 18 6 |—10 
Mean precipitation SNe 1.37] 1.07| 2.49] 2.93] 3.35| 3-38] 3.68] 3.40] 3.06] 4.00] 2.44] 2.38 
Minimum precipitation... 1.07] 0.65} 1.50] 2.45] 2.03] 2.00] 1.36] 2.23] 2.32] 3.09] 1.17] 1.28 
* The temperature r 1 in Fahrenheit and tk ipitation in inch 
frost in autumn was on September 11, 1917. The shortest grow- 
ing period was 87 days in 1917, and ihe longest 106 days in 1919- 
1920, with an average of 98 days. While means and averages 
convey certain pertinent facts, it is the extremes which indicate the 
critical points of climatic influence on vegetation. 
These climatic conditions are adequate to support the maple- 
beech or mixed hardwood formation which are found in typical 
development within the region. * It is apparent, therefore, that the 
yellow-white pine complex is the expression of a combination of 
edaphic factors which exclude the climax type. The main critical 
factor, aside from the question of post-glacial invasion and pre- 
occupation, is undoubtedly the wilting coefficient of the soil. 
Ecological factors 
The ecological factors investigated included soil moisture, 
evaporation, and light intensity. Records were made over a period 
of twenty-eight days, August 3-31, 1918. As August-September 
practically represents the minimum of favorable ecological condi- 
tions for the growing period, the factorial values of either month 
