THE CONICAL GROWTH OF TREES. 63 



growths greatly retarded. One such branch now lies be- 

 fore me, whose principal axis is eighteen inches long, and 

 whose side axes have taken a minimum of development. 



It grew the first throe years five inches annually, or alto- 

 gether fifteen inches ; but in the last four years the growth 

 stagnated, or averaged only nine lines annually ; and the 

 cross-section of the branch actually shows the three inner 

 rings or woody layers, formed by the leaves of the first 

 three years, to be much broader than the four outer rings, 

 the leaf deposits of the last four years. 



The same relation between the breadth of the wood-rings 

 annually formed, and the extent to which the main axis is 

 developed, will still continue to subsist even after the side 

 axes have grown to some considerable extent, provided 

 their growth is accelerated or falls back together with that 

 of the principal axis. If the reader will refer to Figure 2, 

 he will see that the primary axis made a considerable growth 

 the first three years, or between 1852 and 1855, and that 

 from 1855 to 1856, the growth of the axis received a re- 

 markable check, the vegetation of the side axes being re- 

 tarded at the same time. ^Now, let him look at the rings 

 or breadths of the respective cones annually formed, which 

 are represented in the cross-section of the axis at the bot- 

 tom of the diagram, and he will see that the wood-ring or 

 conical stratum of woody matter deposited the fourth year, 

 is much narrower than the other rings. 



It is not, however, always the case in a system of axes, 

 that the growth of the primary and secondary axes advances 

 or falls back together. It not unfrequently happens that 

 the growth of the primary axis is retarded, whilst at the 

 same time some of the secondary axes make considerable 

 headway. Hence, when the primary axis puts forth one 

 or more generations of side-shoots, the growth of each 

 must be taken into consideration in estimating the amount 

 of wood formed by the leaves. A Beech branch, ^for ex- 

 ample, eighteen inches long and nineteen years old, shows 

 on the transverse section of its wood, from within to with- 

 out, sixteen narrow and then three broad, rings. These 

 breadths of the wood-rings do not correspond with the sue- 



