61 



top, and diminishes downwards to some point close to the ground, 

 and then increases again down to the crown of the roots. The 

 rings are thus narrowest at a certain point in the lower part of the 

 stem, which point is. almost on a level with the ground in young 

 trees, but gradually moves upwards with increasing age and the 

 formation of buttresses. In exploitable trees this point is generally 

 situated above the usual height of measuring the diameter, viz., 4$ 

 feet; and in very old trees, and in those which possess free grow- 

 ing-room, it is found'as high as 12 to 24 feet above the ground. 



The increasing width of the annual rings from bottom up- 

 wardsis most marked in favourable soils and localities and in trees 

 in the midst of a dense leaf-canopy {i.e., trees with a long bole 

 acd a small high crown), and least so in unfavourable soils and 

 localities and in overtopping and, especially, isolated trees. It is also 

 most conspicuous in trees that are growing up vigorously, and this 

 particularly in the upper part of tlie stem, whereas, on the contrary 

 in trees pushing up slowly or which have entirely ceased to grow,' 

 the width of the rings diminishes again, towards the top. In the case 

 of isolated trees with low-spreading branches the rings are of the 

 same width thraughoul the entire length of the stem, or may even 

 become narrower from bottom upwards. 



Young trtees have an absolute form-factor of from 0"30 to 0"35. 

 With increasing age these figures rise to 0-44 and even 0*48 ; but 

 they ultimately diminish after an advanced age is reached. This 

 decrease occurs in the European larch at the age of 80 — 100 years, 

 and even earlier in trees, grown out in the open. Trees that have 

 developed in isolation always have a low form-factor. In favour- 

 able soils and localities the form-factor is higher than in unfavour- 

 able ones. 



Tlfe rate at which the stem expands at different heights is ob- 

 viously not the same as that at which the girth increases. The 

 increment of sectional area is greatest at the level of the soil, 

 decreases rapidly upwards for a short distance, then much more 

 gradually up to the beginning of the crown (sometimes even in- 

 creasing in the vicinity of the crown), and lastly, diminishes very 

 rapidly upwards to the top of the crown, where it consists merely 

 of the sectional area of the previous season's shoot. In trees 

 growing in the midst of a dense leaf-canopy, and in those already 

 dominated, the largest increment of sgctional area occurs in the 



