Ill] OF THE GROWTH OF TREES 2^5 



The growth of trees 



Some sixty years ago Sir Robert Christison, a learned and versatile 

 Edinburgh professor, was the first to study the "exact measurement" 

 of the girth of trees*; and his way of putting a girdle round the 

 tree, and fitting a recording device to the girdle, is copied in the 

 " dendrographs " t used in forestry today. The Edinburgh beeches 

 begin to enlarge their trunks in late May or June, when in full leaf, 

 and cease growing some three months later;' the buds sprout and 

 the leaves begin their work before the cambium wakens to activity. 

 The beech-trees in Maryland do likewise, save that the dates are 

 a little earlier in the year; and walnut-trees on high ground in 

 Arizona shew a like short season of growth, differing somewhat in 

 date or "phase," just as it did in Edinburgh, from one year to 

 another. 



Deciduous trees stop growing after the fall of the leaf, but ever- 

 greens grow all the year round, more or less. This broad fact is 

 illustrated in the following table, which happens to relate to the 



Mean monthly increase in girth of trees at San Jorge, Uruguay : from 

 C. E. HalVs data. Values given in ^percentages of total annual 

 increment J 



southern hemisphere, and to the climate of Uruguay. The measure- 

 ments taken were those of the girth of the tree, in mm., at three 

 feet from the ground. The evergreens included Pinus, Eucalyptus 



* Sir R. Christison, On the exact measurement of trees. Trans. Edinb. Botan. Soc. 

 XIV, pp. 164-172, 1882. Cf. also Duhamel du Monceau, Des semis, et plantation 

 des arbres, Paris, 1750. On the general subject see {int. al.) Pfeffer's Physiology 

 of Plants, II, Oxford, 1906; A. Maliock, Growth of trees, Proc. R.S. (B), xc, 

 pp. 186-191, 1919. Maliock used an exceedingly delicate optical method, in 

 which interference-bands, produced by two contiguous glass plates, shew a visible 

 displacement on the slightest angular movement of the plates, even of the order 

 of a millionth of an inch. 



t W. S. Glock, A. E. Douglass and G. A. Pearson, Principles ... of tree-ring 

 analysis, Carnegie Inst. Washington, No. 486, 1937; D. T. MacDougal, Tree Growth, 

 Leiden, 1938, 240 pp. 



% Trans. Edinb. Botan. Soc. xviii, p. 456, 1891. 



