CONTENTS. VII 



The Climatic Conditions of the United States— continued. paqb. 



III. Moisture conditions — continued. 



3. Removal of water from plant — continued. 



D. Aqueous-vapor pressure. 



(1) Preliminary considerations 344 



(2) Normal mean aqueous-vapor pressures for the period 



of the average frostless season (table 19, plate 63) . . 344 

 Table 19. — Normal mean relative humidities, for 

 year and for period of average frostless season, 

 mean relative humidities for the three summer 

 months, 1908, and normal mean vapor-pressures 

 for the year and for period of average frostless 

 season 344 



(3) Normal mean aqueous-vapor pressure for the year 



(table 19, plate 64) 349 



E. Relative air humidity. 



(1) Prehminary considerations 349 



(2) Percentages representing normal mean relative air 



humidity for period of average frostless season 

 (table 19, plate 65 and fig. 17) 351 



(3) Percentages representing normal mean relative air 



humidity for the year (table 19, plate 66) 354 



(4) Percentages representing mean relative air humidity 



for June, July, and August 1908 (table 19, plate 67). 354 



(5) Generalizations from the three charts of relative humid- 



ity values (plates 65 to 67 and fig. 17) 355 



F. Wind (table 20, plate 68) 359 



Table 20. — Average wind velocities for the year 

 and for the period of the average frostless 

 season 360 



G. Sunlight as a condition influencing water-loss from plants 



(table 21, plate 69) 363 



Table 21. — Normal total number of hours of sunshine 



within the period of the average frostless season 369 



IV. Moisture-temperature indices. 



A. Introductory 370 



B. Moisture-temperature indices based on temperature summa- 



tion-indices obtained by the remainder method (above 39° 

 F.), for the period of the average frostless season (table 22, 



plate 70) 371 



Table 22. — Moisture-temperature indices for the period 

 of the average frostless season, by remainder (above 

 39° F.), exponential, and physiological methods 373 



C. Moisture-temperature indices based on temperature summa- 



tion-indices obtained by the exponential method, for the 

 period of the average frostless season (table 22, plate 71) 375 



D. Moisture-temperature indices based on temperature summa- 



tion-indices obtained by the physiological method, for the 

 period of the average frostless season (table 22, plate 72, 

 and fig. 18) 375 



E. Conclusions from the study of the three forms of moisture- 



temperature products (fig. 18) 375 



V. Cartographical combination of temperature and moisture indices 



(fig. 19) 379 



VI. General conclusions from the study of climatic conditions in the United 



States 381 



A. Temperature conditions 383 



B. Moisture conditions 384 



C. Combinations of temperature and moisture conditions 386 



