

iQi7l GANO— ECOLOGY OF FLORIDA 



339 



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68 , winter 53 , and spring 67?6 F., indicating a moderate and 

 equable yearly temperature. There are records of severity, how- 

 ever, the lowest temperature for the state being recorded from Leon 

 County, — 2 F. on February 13, 1899. Frost may be expected 

 from November 1 until April 1, the frost record for 18 years giving 

 the date of the first killing frost in autumn as November 4, the 

 last killing frost in spring as April 6, the average date of the first 

 killing frost in autumn as December 5, and the average date of the 

 last killing frost in spring as March 3. 



The mean annual precipitation for the Tallahassee station (3) 

 is 57.12 inches, and there are 2 marked periods of rainfall; one 

 (the lesser) in winter culminating in March, and the other (more 



excessive) culminating in July. This summer rainfall averages 

 26.8 inches, and the winter rainfall 17.9 inches, the summer rains 

 occurring almost daily as afternoon thunderstorms, while the winter 

 rains are more evenly distributed between day and night. The 

 year is divided thus into wet and dry seasons, more or less marked, 

 April and November being the driest months. 



There are no reliable records for relative humidity, although for 

 northern Florida the percentage of relative humidity is highest in 

 September and lowest in April. 



These climatic effects combined tend to make spring (April 

 period) the hardest season for plants, so far as the moisture rela- 

 tions are concerned. 



Physiography. — Limestones of the Oligocene period are con- 

 sidered now to be the oldest rocks of Florida and to form the rock 

 basis for most of the state (9). These limestones also are the sur- 

 face rock over much of northern Florida, and indicate the earliest 

 and most persistent land surface during subsequent geological 

 history. The presence so near the surface of readily soluble and 

 easily disintegrated rock has doubtless had important influence 

 upon the present topography and drainage, as well as upon the 

 character of some of the soil. 



Crossing the country from north to south, the most striking 

 topographical feature is the division of the surface into 2 distinct 

 parts, a highland and a lowland. By this division about two-thirds 

 of the surface is included in the highland, which is a portion of the 



