INTERPRETATION OF THE CURVE OF THE SEQUOIA. 



169 



In each of these four cases we have a group of favorable years to ])e compared with a group 

 of unfavorable. The comparison can most easily be made by means of a series of diagrams 

 showing the average amount of rain for each month in each group of years. This is done 

 in figure 49, where the solid lines represent the favorable years, the dash lines the un- 

 favorable, and the intermediate dotted lines the mean for all years. The dates and figures 

 on which the curves are based are given in tables 7 and 8. From table 7 it appears that 

 29 years are included in one or another of the favorable groups; 18 of these are included in 

 only one favorable grouji, 3 are in two groups, 2 are in three groups, and 6 are in four. 

 The unfavorable groups include 35 years, 20 of which are included in only one group, 9 

 in two, 2 in three, and 4 in four. Only 10 years fail to fall in any group, while 12 fall in 

 both a favorable and an unfavorable group. One of these last, 1874-75, falls in one 

 favorable group and two unfavorable. Omitting all years which fall in only one group, 

 or in both favorable and unfavorable groups, there remain 11 which fall in two or more 

 favorable groups and 14 which fall in two or more unfavorable groups. These 25 years 

 form two final groups (E in the tables) representing the extremes of the two conditions 

 with which we have to deal. The average monthly distribution of rainfall in them has 

 been plotted as the last of the sets of curves in figure 49, and may be regarded as the most 

 typical. 



Table 8. — Mean tiDntklij riunfnll (in inches) of Ihc ijroujis of favorable an-l uiifarorable years shown in table 7. 



A comparison of the curves of figure 49 is interesting. In group A, IG years with 12 

 inches of rain are compared with 14 having less than 8 inches. Both curves are here quite 

 regular, and in general form resemble the mean curve for the entire 60 years since records 

 have been kept. In all three precipitation increases from July to December, and decreases 

 from January to June, the only marked exception being February in the curve for years 

 of low rainfall. The work of Professor KuUmer, as explained later, shows that during 

 the favorable years of this group the storminess of the United States as a whole slightly 

 exceeded the average, while during the unfavorable years it was distinctly less. The 

 next set of curves indicates the distribution of precipitation during 14 years of uncom- 

 monly favorable growth and 12 years of uncommonly unfavorable growth, no attention 

 being paid to the amount of rainfall. The position of the curve for the favorable years 

 above that for unfavorable years from November to April, inclusive, indicates that 

 the growth of the trees is strongly influenced by the amount of rain during the preceding 

 winter. But the fact that these two curves are much closer to one another than are the 

 two representing groups of years selected solely upon the basis of rainfall emphasizes the 

 conclusion already reached that the amount of growth depends upon the rainfall of a con- 

 siderable number of past years, not upon that of one year alone. The next two sets of 

 curves represent 12 favorable and 12 unfavorable years selected because of the criteria 

 mentioned under C, and 9 favorable and 17 unfavorable years of the type D. Inasmuch 

 as both of these sets are based on the relation of rainfall and growth rather than upon either 



