16 



Transactions. 



8 ft. 3 in. in diameter, and which had a cavity in the centre quite 18 in. across, 

 had its external rings of growth perfectly well developed, the last twenty- 

 five occupying a space of very nearly 2|in., a rate of growth equivalent 

 to 10-0 rings per inch of radius. This proportion is only very slightly 

 under my general average of 9-7, and is well within the range of variation 

 likely to occur. 



A further word or two may be expected in reference to Kirk's idea that 

 " the immense pressure exerted by the outer cylinders consolidates the 

 inner part of the trunk so that the number of rings to the inch is greatly 

 increased." But in making this statement he overlooked the immense 

 strength and rigidity possessed by a column of woody tissue like that of 

 a young kauri, say, 250 years of age. The already completed rings of 

 growth, and especially those constituting the heart-wood, or duramen, have 

 had the walls of their tissues thickened and hardened to such an extent as 

 to constitute a framework, or skeleton, capable of withstanding any pres- 

 sure that can be exercised by a newly formed woody layer. No doubt each 

 new layer during its formation is subjected to varying strains and stresses, 

 which modify its structure, and which, among other things, produce the 

 well-known differences between the spring and autumn wood ; but room 

 for its actual formation is provided by the expansion of the inner cortical 

 tissues, and the consequent Assuring or throwing-off (as in the case of the 

 kauri) of the dead outer cortex. I conclude that Kirk was mistaken in 

 supposing that previously formed annual rings could be materially reduced 

 in thickness by the formation of rings of later growth, and submit the 

 following experimental proof. The tabular statement already given shows 

 the annual rings of growth in twenty-nine sections varying from 6 in. to 

 11 ft. in diameter. I propose to divide these sections into four groups, as 

 follows : First, those with a diameter under 2 ft. ; second, those from 2 ft. 

 to 4 ft. ; third, from 4 ft. to 6 ft. ; fourth, from 6 ft, to 11 ft. The result 

 is seen in the subjoined table. 



General average for the whole of the groups : 9-7. 



The above table shows no evidence of the number of rings to an inch 

 being " greatly increased " in mature trees The averages for the various 

 groups vary by only 2-4; and the average for trees between 6 ft. and 11 ft. 

 in diameter, which would surely be called mature, is precisely the same 

 (10-9) as that for trees between 2 ft. and 4 ft., and is very far removed from 

 Kirk's suggested rate of thirty per inch for a 7 ft. tree. 



Irregularities in the rate of growth of individual trees, however, are not 

 uncommon, and may occur at any period of the life of the tree. It may 

 be interesting to give a table of the rate of growth of an 11 ft. tree, the 

 largest I have measured, and which, curiously enough, was also the most 

 irregular in growth. For comparison I have included a similar table of 



