ENVIRONMENT 103 



eter, but is only about 1,500 years old. That rapid growth is the 

 effect of contact with an unfailing source of water. 



SEQUOIA TOPOGRAPHY 

 In selecting specimens to settle a dating problem, in 1919, prefer- 

 ence was given to trees at such distance from the obvious water- 

 supply that the specific dependence of trees on the nearby brook 

 could be tested. Thus from Redwood Basin, 15 miles east of the 

 General Grant Park, a total group of 21 sequoias was obtained. The 

 trees were scattered for a mile along this valley, whose slope faced 

 the north. The upper or southern end is near the top of the moun- 

 tain, but a spring supplies a small stream of water. The upper 

 trees mostly had a very dry soil, while those below, some 600 or 

 700 feet in vertical measurement, had more level ground and greatly 

 increased moisture. The average growth per century in the last 500 

 years was about 7.6 cm. The least was less than 4 cm. and the greatest 

 was over 15 cm. The fast-growing trees were mostly close to the 

 water-course in the lower basin. The average growers were mostly 

 around the edges of the basin, while the slow-growing trees were 

 chiefly at the tops of the slopes. Three larger growing trees close to the 

 upper limit formed interesting exceptions. One was a youthful 

 sequoia, only 700 years old when cut, and therefore naturally a fast- 

 growing tree. Another at the very highest point was about 50 yards 

 above the spring and undoubtedly tapped an underground flow of 

 water leading to it. Its type of rings was very similar to those in the 

 basin. The third exception had very large rings, but they were full 

 of sensitive variations like the slow-growing trees nearby. This 

 tree is probably over a pocket of water whose help increased its growth, 

 but which failed in extremely dry conditions. It is evident, then, 

 that with the sequoias moisture may control the growth up to a 

 maximum fully four times as large as the minimum. 



Ring-type and moisture — The type of ring and its adaptation to 

 identification and study varies greatly with the moisture-supply. 

 The large rings of the quick-growing trees are either very complacent, 

 that is, of the same size for many years in succession, or gross in 

 character, which means extraordinarily large rings here and there; 

 and their whole grouping is apparently subject to slow surges in size 

 as one glances across the sequence from center to bark. Gross rings 

 in one tree have about an equal chance of appearing or not appearing 

 in any other tree near by. Since gross and complacent rings have little 

 individuality, it is not always easy to identify their dates, especially 

 if the outer layers of wood have been cut away, as was usually done 

 in felling the sequoias. On the other hand, the slow-growing, low- 

 moisture trees are full of irregularities which may be recognized in 

 tree after tree, thus rendering accurate dating a remarkably easy 



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