CLIMATE 57 



The ratio of the growing to the non-growing portion of 

 the year is graphically shown in Pig. 8, which applies to sev- 

 eral stations at altitudes varying from 1880 to 6200 feet. For 

 each station a base line is drawn representing 40 degrees F., the 

 approximate minimum of temperature as related to seasonal 

 vegetative activity. Above and below parallel lines are drawn 

 at intervals of ten degrees. Each diagram thus represents a 

 vertical range of temperature of from 40 to nearly 60 degrees. 

 The mean temperature for each month is fixed by points above 

 and below the base. A line drawn through these points forms 

 a seasonal curve for the temperature of the station. This curve 

 falls billow the base during the winter months. Descending 

 sharply it reaches the minimum sometime in January, then it 

 ascends. crossing the line usually in April, and reaches the 

 maximum in July, whence it sinks again to the base line in 

 October or November. Between the curve thus described and 

 the base are included two areas, one above and the other below, 

 which together represent respectively the positive and the neg- 

 ative temperature conditions of the year. They represent also, 

 from the standpoint of vegetation the relative values of the 

 months indicated. 



The vertical lines separate the months. The mean tem- 

 perature for each month is fixed at the middle or half way be- 

 tween the verticals. On some of the curves these points are 

 marked and indicated by figures expressing the mean tempera- 

 ture of the months. (Figs. 8, 9.) The relative lengths of the 

 growing and the non-growing seasons can readily be compared. 

 In some cases the two periods are seen to be about equal, six 

 months of each. In others, the ratio is 5 to 7 in favor of the 

 growing season. The vertical distances determine the areas which 

 are proportional to the values of the periods. In comparison the 

 growing seasons are seen to have relative values of 7, 8, 9, 11, 12, 

 14, etc., in different parts of Montana, as reckoned by the total 

 areas of the squares. While the curve is a generalized one and 

 the actual temperature variations would show sharp oscillations 

 above and below, the areas included may, in the long run, be 

 taken as fairly representative of the seasonal values. 



Livingston (35) has suggested a method of reckoning tem- 

 peratures in relation to field vegetation according to exponential 



