CLIMATIC CONDITIONS OF THE UNITED STATES. 205 



dates accredited with normals of 32° or below occur consecutively. 

 Thus the period so characterized may be termed the normal season of 

 cold weather. 



Our method of procedure in the present case brings out the fact thaf 

 nearly one-half of the United States is without such normal periods of 

 cold weather as are here considered. The longest period encountered 

 is of 158 days. The numbers obtained from this study are shown in 

 table 3, and the chart of plate 36 exhibits the equiseasonal lines 

 derived therefrom, this chart thus exhibiting graphically the extent of 

 the areas having different lengths of cold season as here characterized. 

 The station locations are again indicated by small circles on the chart. 

 Increments of 30 days have again been employed, as in the charting of 

 the periods of hot days (plate 35) . 



From plate 36 it is seen that the area indicated as without cold season 

 occupies the entire country south of a line passing, approximately, 

 from Cape May, New Jersey, to Tucson, Arizona, and is extended 

 westward and northward to embrace approximately the southern 

 third of California, the western two-thirds of the remainder of that 

 State, and the western half of Oregon and of Washington. It is in this 

 area that the most highly reputed winter resorts occur. 



The area characterized by 150 or more days of normal daily means 

 of 32° F. or below occupies only the northern third of Minnesota, the 

 northern half of North Dakota, and a little of northeastern Montana. 



The eastern mountains and the Great Lakes appear to have little 

 tendency to extend the areas of cold winter weather southward, but 

 such an effect is noticeable in the case of the western mountains. The 

 influence of the Pacific Ocean is conspicuous, crowding the area of cold 

 season far back from the coast, even north of the Canadian boundary. 



2. INTENSITY OF TEMPERATURE CONDITIONS. 

 (A) PRELIMINARY CONSIDERATIONS. 



The physical conception of life phenomena allows us to regard the 

 organism as a spatial system, in which a complex series of chemical 

 and physical changes are ever in progress; during life, material and 

 energy are always entering the system and are as unceasingly leaving 

 it. The accomplishment of growth, maturation, reproduction, etc., 

 of a plant is thus to be regarded, at any moment in its history, as the 

 summation of the effects produced by the innumerable physical and 

 chemical changes which have thus far occurred. Since all energy and 

 material transformations are influenced to a greater or less extent by 

 temperature, and since this influence is usually very important, it 

 follows that, if other conditions were but constant, or if they always 

 varied in the same manner, the state of a plant at any moment might be 

 treated almost as a direct function of the various aerial temperature 

 conditions to which it has been subjected in the past. Of course the 



