42 ILLINOIS STATE ACADEMY OF SCIENCE 



were four years that the temperatures did not get as low as 

 zero and with an average of almost exactly zero for coldest 

 days. In 1912 and 1918 the temperature reached 24 degrees 

 and 18 degrees below zero. These great extremes of tem- 

 perature are due to the inland position of this section and 

 to the fact that the low Central Plain of North America 

 affords no obstruction to either the cold waves from the 

 north or the hot winds from the south. The seriousness of 

 these extremes is seen in the cold waves of 1912 and 1918 

 when the peach and other tender fruit trees of the Ozark 

 region were seriously "winter killed." 



The average mean July temperature for the last ten years 

 is 80.04 degrees ; the mean average for January temperature 

 for the same period is 34.3 degrees. The average date of 

 the first killing frost in the fall is October 25, and the aver- 

 age date of the last killing frost in the spring is April 9. 

 This gives the average period free from frosts, six m.onths 

 and sixteen days. These are very important factors in de- 

 termining the time of year that both fruits and vegetables 

 can be placed on the city markets. But few summer apples 

 reach the northern markets earlier than those from the 

 Ozarks. The temperatures that the fruit and vegetable 

 grower notices most, however, is the suddenness of temper- 

 ature changes, particularly in the spring. A few warm days 

 in March, or early April, often cause the fruit buds to burst 

 into bloom; then comes a sudden cold wave which in one 

 night will change a promising fruit crop to almost a failure. 

 These spring freezes are the temperature changes that the 

 fruit grower dreads most of all. Complete failures of the 

 fruit crops are rare however, particularly of the hardier 

 apples and small fruits. This is especially true in the high- 

 er parts of the Ozarks where the frost drainage is best and 

 where the fruit industry is extensively and scientifically 

 carried on. Even this spring of 1921 there is some fruit in 

 the higher parts of the Ozarks, notwithstanding the fact 

 that on March 24 and April 11 the temperatures were 24 

 degrees and 26 degrees. Some growers report from 20% 

 to 75% of a crop for the hardier apples, and almost every- 

 where from 50% to 75% of a berry crop. The strawberries 

 are about 50% and blackberries 75%. 



