256 OHIO BIOLOGICAL SURVEY 



January and sometimes in February. The data do not include, how- 

 ever, the extremely hot summer of 1911, nor the exceptionally cold 

 winter of 1911-12. The extreme temperatures recorded for the middle 

 section of the state, 108°aud -34°, will perhaps give a better idea of 

 what may be expected for the absolute extremes in our area. These 

 are of course important because of their destructive effect on vege- 

 tation which would tend to control the southern limits of certain 

 species and the northern limits of others and so react on the compo 

 sition of the flora. 



The average date of the last killing frost in spring is April 30. 

 of the first killing frost in the autumn October 2. The average growing 

 season is therefore about 155 days in length. But the latest killing 

 frost reported was on May 30, and the earliest in autumn about Sep- 

 tember 15, giving a minimum growing season, if both late and early 

 frosts should occur in the same year, of only 110 days. But the frost 

 data have not been taken for a long enough period at any of the sta- 

 tions under consideration to give reliable data as to possibilities in this 

 direction. "On June 5, 1859, a killing frost occurred in the central 

 and northern part of this section [i. e. Sec. 71] that is still known as 

 the great June frost." 



'' Precipitation is quite uniform over the whole of the section [in 

 which our area is located] and averages about 38 inches (95 cm.) per 

 year. At North Lewisburg in Champaign County the smallest annual 

 rainfall in a period covering 56 years was 23 inches (57.5 cm.) in 1872, 

 and the greatest 58 inches (145 cm.) in 1852," while at Cincinnati in a 

 record from 1835 to 1908 inclusive, the least was 17.99 inches (42.5 

 em.) in 1901 and the greatest 65.18 inches (163 cm.) in 1847. "The dis- 

 tribution of the rainfall is fairly uniform, as ^vill be seen from the table 

 given herewith." "In general there is the greatest average rainfall in 

 June and July, and the least in October. There are very few months 

 with less than an appreciable amount of precipitation in all parts of 

 the section, and monthly falls of over 10 inches (25 cm.) are not very 

 frequent. The greatest monthly fall reported at any of the stations 

 under consideration is 15.90 inches (40 cm.) at North Lewisburg in 

 September, 1866," while at Carthegena, Mercer County, 17.33 inches 

 (43 cm.) fell in June, 1877. Although these stations are at consider- 

 able distances fi-oni tlie area under consideration, their records will give 

 a fair idea of the maximum precipitation to which its vegetation would 

 be subjected in a long series of years. This extreme maximum is of 



