410 ANNUAL EEPOET SMITHSONIAN INSTITUTION, 1912. 



climatically similar to New Mexico, except that it is colder and has no 

 rainy season in summer. Long, snowy winters and rains continuing 

 well into the dry summer are the conditions which favor growth. 

 The curve of the sequoia has been computed in the same way as that 

 of the other trees. The period covered by the growth of the trees, 

 however, is so great that the number of trees whose analyses are now 

 available is not enough to give certainty to the corrections. Accord- 

 ingly, after obtaining a curve corrected as accurately as possible both 

 for age and longevity, I have tilted the whole line slightly in order 

 to make the relative height at tliree or four fixed points correspond 

 as nearly as may be with the height of the Caspian Sea at the same 

 dates. This, however, has no effect upon the sinuosities of the curve, 

 but merely upon the exact amount by which the earlier parts are 

 higher than the later. Before we proceed to discuss the curve a word 

 or two of explanation may be added. The horizontal lines indicate 

 the growth in millimeters per decade. The extreme fluctuations of 

 the early part of the curve give an exaggerated idea of the variability 

 of the climate at that time. This is due to the small number of trees 

 available. When more have been measured the extremely sharp char- 

 acter of the depressions and hollows, or of the arses and theses, as I 

 have elsewhere called them, will disappear. 



Examination of the curve shows that the climate of the interior of 

 California has been subject to marked pulsations during the past 

 3,000 years. For instance, at the time of Christ the tree grew 30 

 per cent faster than at the end of the fifteenth century. Practically 

 all the trees at the latter date were of large size with thoroughly 

 developed root systems, and mth a vast supply of strength stored up 

 from the past. Moreover, they were growing high among the moun- 

 tains where the supply of ram and snow was largest, and many of 

 them were standing in swamps or beside brooks. If they could be so 

 affected by drought as to show a decrease of 30 per cent in the amount 

 of growth, other less favored plants must have suffered much worse. 

 It is noticeable that in general the trees recover rapidly after a period 

 of aridity and then fall off more slowly as another dry time approaches. 

 This is important as an indication that climatic changes from dry to 

 moist take place rapidly, while those in the reverse direction are slow. 

 It bears also on another point. It may be suggested that the inequali- 

 ties in the curve are due to accidents such as fires. In the first place, 

 this is not probable, since the 451 trees were located in four different 

 areas with a distance of 60 miles between the extremes and with high 

 mountauis and deep valleys intervening. The rapid rise and gradual 

 fall of the curves, however, disproves any such supposition. An acci- 

 dent, such as a fii-c or anything else, would suddenly cause the trees to 

 grow slowly, after which they would gradually recover, whereas the 

 actual case is the reverse of this. 



