548 



CORRELATION OF DISTRIBUTIONAL FEATURES. 



Magnolia grandifiora (fig. 56). — The distribution of this magnolia 

 covers only the portion of the Coastal Plain between Cape Fear and 

 the Trinity River, and south of the northern boundary of Louisiana. 

 This is a region with no cold days, in our sense, and with high ranges 

 for all of the temperature conditions studied. It is also a region with 

 a high normal daily mean precipitation, although the amplitude of 

 this condition is not great. The amplitude in number of days of both 

 the wet and the dry periods is very wide, and those of evaporation, 

 humidity, and the moisture ratios are narrow. 



The range of Magnolia is remarkable from the fact that its limit 

 corresponds with a large number of isoclimatic lines, giving the follow- 

 ing indications regarding the conditions which it encounters : a f rostless 

 season of 240 days or more, a normal daily mean temperature of 45° 

 or more for the coldest 14 days of the year, an annual mean temperature 

 of 65° or more, a mean relative humidity in the frostless season of 65 

 per cent or more, and a value for the moisture-temperature index of 

 15,000 or more. None of the isoclimatic lines for moisture conditions 

 coincide, even roughly, with the limit of Magnolia, although the 

 narrow amplitudes of evaporation, moisture ratios, and humidity 

 indicate that this tree encounters only a small part of the total range 

 of these conditions for the United States. The limit of Magnolia 

 corresponds rather closely with the line to the south of which are found 

 5 or more species of evergreen broad-leaved trees (see plate 3), and the 

 climatic characteristics just mentioned may be taken as defining the 

 region which is favorable for the abundant occurrence of trees of this 

 type. 



TCMPCHATUHC 



D»« IN No<tM*L FnotTLtt* SC««ON <F. S.I 

 Hot Davc, F. S. 

 Coio D*v«, F. S. 



PhTSIOLOOICAL SUMMkTION, F. S. 



Normal Dailt Mean, colokst 14 days or Ycau 



Normal Daily Mcan, Ykar 

 Prcciritatioh 



Normal Daily Mcan. F. S. 



Days in lonocst Normal Rainy Period, F. S. 



Day* in lonocbt Normal Dry Period, F. S. 



Mean Total. Year- 

 Evaporation 



Daily Mean. 1867-8, F. S. 

 Moisture Ratio* 



Normal P/e. F. S. 



Normal it/Z, F. S. 



Normal P/E, Year 

 Humidity 



Normal Mean, F, S. 

 Sunshine 



Normal Daily Duration, F. S. 

 Moisture-Temperature Indices 



Normal P/E x T, F. 8., Pmysiolocical Method 



Fig. 56. Climatic extremes for Magnolia grandifiora. 



