GROWTH IN TREES.i 



By D. T. MACDOUGAL. 



(Read April 21, /p-'/.) 

 (Plate I.) 



My studies of the course and physical conditions of growth were 

 extended to inckide the changes in circumference and diameter of 

 tree trunks as well as the elongation of growing branches in 1918, 

 and a new technique with specially designed instruments was found 

 necessary for the analytical study of the changes in volume of these 

 massive organs. The records are now continuous for a large num- 

 ber of trees for many months, one tree having been under continu- 

 ous measurement since September, 1919.- 



Two new instruments were designed for obtaining measure- 

 ments of growing trees. The dendrograph, an instrument for mak- 

 ing continuous records of the variation of tree trunks, is an instru- 

 ment consisting of a floating frame of metal of low temperature 

 coefficient, such as invar or bario, which may be placed around a tree 

 trunk, and the variation in distance between a contact rod on one 

 side of the trunk and of one end of a rod or lever on the other side 

 is traced by a pen on the free end of a lever on a sheet of paper car- 

 ried by a recording cylinder. Such measurements are in terms of 

 the diameter. In an earlier form of the instrument two levers were 

 employed. One end of a bearing lever was placed in contact with 

 the tree, the free end being linked to the short arm of the recording 

 lever. The results previous to October, 1920, were obtained by 



1 The full paper of wliich this is a synopsis will be published by the 

 Carnegie Institution of Washington as prospective No. — of its series. 



2 MacDougal, D. T., " The Dendrograph ; a New Instrument for Record- 

 ing Growth and Other Variations in the Dimensions of Trees," Carnegie 

 Inst. Wash. Year Book for 1918, pp. 59-60. " The Dendograph." xhid., for 

 1919. PP- 1^-1^- " The Coure of Growth in Trees as Measured by the Den- 

 drograph," ibid., for 1920, pp. 51-52. " Measurement of a Season's Growth 

 of Trees by the Newly Designed Dendrometer," ibid., for 1920, p. 52. 



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