456 Mr Charles E. Hall on 



Notes on Tree Measurements, made Montlily at San Jorge, 



Uruguay, from January 12, 1885, to January 12, 1890. 



By Chaeles E. Hall, of San Jorge. (Plates V. 



and VI.) 



(Read 12th June 1890.) 



In 1885 I began measuring the girth of twenty-eight trees 

 every month at San Jorge, in the republic of Uruguay, in 

 lat, 32° 43' S. and long. 56° 8' W., and own a debt of grati- 

 tude to Dr Christison, of Edinburgh, for having suggested to 

 me a work which, interesting at first, has become more so 

 each succeeding year. 



My measuring day was almost invariably the 12th of 

 each month; never earlier than the 11th and never later 

 than the 14th. The trees are marked with a light-painted 

 line, not half encircling the tree, at 3 feet above ground 

 level; this is the measuring point. The measure used is a 

 steel tape, marked to millimetres. When a measurement 

 appeared doubtful it was repeated. The repetition of a 

 measurement, in the case of rough-barked trees, was not 

 found invariably to exactly corroborate the first measure- 

 ment taken ; but a discrepancy of 2 millimetres, or the 

 thirteenth part of an inch, was cause enough for a third 

 measurement being taken. Until the last ten months I 

 have, with but four or five exceptions, taken the monthly 

 measurements myself, but have frequently been accompanied 

 and sometimes had my measurements corroborated by others. 



I have been in the habit of noting the difference between 

 dry and wet bulbs of a hygrometer at time of measurement, 

 generally when I was half way through the measuring work, 

 fancying that the humidity or dryness of the air may have 

 some effect on the stiffness of the bits of lichen on the bark 

 of a few of the trees or on the bark itself, and thus probably 

 affecting actual girth-measurement. I made two or three 

 trials as to this by measuring in early morning, when the 

 air was nearly saturated with moisture, and again about 

 3 P.M., when there was a large difference between wet and 

 dry bulbs. I have unfortunately lost or left at San Jorge 

 the records of these trials ; but what I remember about them 



