CLIMATIC FACTORS 61 



United States Weather Bureau, shows the average length 

 of the crop-growing season, or rather the time between the 

 average date of the last killing frost in spring and the 

 average date of the first killing frost in fall. 



The growing season of corn nearly coincides with the 

 last probable frost of spring and the first probable 'frost of 

 fall. For example, at Lincoln, Nebraska, where the aver- 

 age time between killing frosts is given as 165 days, it is 

 not considered advisable to grow a variety of corn taking 

 more than 130 days to mature. The growing season for 

 corn would be, in general, 20 to 30 days less than indicated 

 on the chart ; or the 200-day limit would be^ central South 

 Carolina. 



Also, there is great fluctuation in the length of growing 

 season from year to year at any one point, and there is a 

 general tendency to grow corn that will mature in the 

 shortest season. Frear ' made a study of meteorological 

 conditions in relation to the development of corn at the 

 Pennsylvania station for three ears, 1887 to 1889. In 

 his conclusions he makes this statement : " The difference 

 in temperature between these two seasons (1887 and 1889) 

 is almost equal to the difference in the mean July tempera- 

 ture of Quebec and Boston ; of Burlington, Vermont, and 

 Philadelphia; and of Fort Assiniboine, on the northern 

 boundary of the United States, and Santa F6, New Mexico. 

 Then, too, in 1889 the rainfall was almost twice as great as 

 in 1887, and the cloudiness at least 25 per cent greater." 



48. Relation of sunshine to growth. — The function 

 of sunlight in furnishing the necessary energy for the 

 various activities of plant growth was discussed in the 



' Fbeab, W., and Caldwell, W. H. Relation of Meteorological 

 Conditions to the Development of Corn. Penu. Agr. Exp. Sta., Ann. 

 Kpt. 1889. 



