July. 1920.] 



OGURA -.—GROWTH IX THICKNESS. 



93 



My materials from Mt. Kiyosumi (No. I — III) were also planted 

 trees, and showed quite the same type of growth, the difference being 

 onlv in the degree of growth. A few rings in the center were obscure 

 and thin ; further outw T ards the thickness of rings gradually increased 

 outwardly, until the maximum in- the fifth or sixth ring, then decreased 

 very slowly in subsequent rings. A certain portion of wood made up of 

 a number of rings in the center corresponds the time of elongation rather 

 than the growth in thickness, and may be called the "young stage" of 

 thickening growth. This entire growth may be expressed by a curve, 

 if we take the number of years of growth as ordinates and the an- 

 nual increase in thickness as abscissae (Art. Jap., p. (14:9), Fig: l 1 ). 

 Though such a curve is very irregular in part, it shows as a whole a 

 certain period of increase in the center, and then gradually falls in the 

 following stage. As the form of the curve drawn in this way. however, 

 can not be suitably expressed by a formula, another type of curve will 

 be drawn by taking the entire radii from the center or pith as abscissae. 

 The latter curve will be called the "radial curve" of growth in thickness. 



Weber 2 gave the formula D = \ — - for the diameter increase, in 



which p is a constant which varies, however, according to the rate of 

 growth of individual trees ; D, the dia- 

 meter corresponding to the age x, x Table I 

 being the age in years X. from which i> :il \i A } curve of ' No. I) 

 the age in years in the slow thickening 

 stage i has been subtracted. Honda 

 reported that the formula could be ap- 

 plied to Cryptomeria japonica from Ki- 

 yosumi district in Japan. 



In the present investigation for the 

 three samples of Cryptomeria from Ki- 

 yosumi, I adopted X instead of x. and 

 used modified form of the Webek's for- 

 mula, viz. R — \ — — , in which R is the 



radius of the corresponding ring A", in- 

 cluding the growth in the young stage. 

 Table I is an example of the application 

 of this modified formula for the material No. I (X, age in years : r, 



! B 





-1 p 



= 20 



X 



r 



R 



1 



10 



6.81 



6.95 



+0.14 t 



80 



10.02 



•_- 





30 



12.42 



12.75 



+ 0.33 J 



40 





14.95 



-0.11 



50 



16.70 



16.80 



+0.10 



60 



17.94 



IS. 50 



+0.56 



70 



18.73 



20.00 



+ 1.27 



SO 



19.30 



_. 



-2.20 j 



1. Growth curves of Cryptomeria, taken in every five years. 

 Ill; C. No. V; D, No IV; E, No. VIII: F, No. IX. 



2. "Weber, E. (1891] Lehrbuch der Forsteinriehtung. — Berlin. 



A, No T; B No. 



