State Board of Forestry. 51 



by the temperature element. Due consideration must be given to 

 the highest and lowest temperatures reached in the locality under 

 discussion. The temperature has a comparatively wide range, as 

 the State of Indiana comes well within the influence of the pro- 

 nounced cold waves which occasionally sweep down from the north- 

 west over the central valleys. The distance from any large body 

 of water is sufficient to prevent modifying influences from that 

 source in either summer or winter, except over a small area in 

 the extreme northwest corner bordering upon Lake Michigan. The 

 temperature at all stations occasionally rises in summer to 95 de- 

 grees or more, but these instances are rare. The hot periods are 

 generally of short duration and interspersed with those of moder- 

 ate temperatures and cool breezes, which tend to greatly lessen 

 the effect of the summer heat and produce a climate that is de- 

 lightful rather than oppressive. It frequently oecurs that the high- 

 est temperature of a season is recorded in the central or northern 

 part, while the lowest is sometimes recorded at a station well 

 toward the southern end of the State. This is due to the fact that 

 the areas of high and low barometric pressure, which produce these 

 extremes of temperature, cross the State with as great frequency 

 over one portion as the other. It may so happen that, during a 

 hot wave, the heat is more intense in the northern half of the 

 State, while on the other hand, a cold wave may be more severely 

 felt in the southern half. It is also true that the records of in- 

 dividual stations are more or less affected by local topographic 

 features. The lowest temperatures reached during a season, or 

 period of years, have a greater effect upon the character of vege- 

 tation than do the highest temperatures. 



The length of the growing season has a more direct and de- 

 cisive influence than is exerted by the minimum temperatures. A 

 chart (Plate 4), showing the advance of spring is presented here- 

 with. It will be noted that the average date of last killing frost 

 at Evansville is April 7th. A week later the line has moved north- 

 ward until it includes the greater part of what is termed ^'The 

 Pocket" of Indiana. In another week about one-third of the State 

 is included, and week by week the line moves northward until on 

 ]May 5th there remain only small areas in the northern and eastern 

 parts of the State where there is still a probability that a frost 

 sufficient to kill the staple products of those localities will occur. 

 It maj^ also be observed that the distribution outlined on this chart 

 bears a fairly close resemblance to that shown on the chart of an- 



