-206 Ewart and Tovey : 



Xhe changes in circumference lag six to twenty-four hours behind 

 the changes of temperature. Ihe temperature at the centre of the 

 trunk of a large leafless tree is not, however, affected appreciably 

 by daily variations of temperature, and only responds slowly to a 



• change in the average mean temperature. 



In the measurements of the Elm taken in 1917-18, it was found 

 that an apparent growth contraction took place in winter, and 



.that slight variations in circumference were shown from time to 

 time during the non-growing period. These measurements were 



.taken with' a tape around a partially smoothed line. 



To obtain moie accurate measurements a girdle of bark w^as re- 

 moved, leaving a smooth surface close to the cork cambium. A 

 standard length of 6 ft. 9 in. was marked by Dr. Baldwin, Govern- 

 ment Astronomer, on the stone basement. After each measurement 

 with a waxed tape it was extended over the standard, 'the increase 



.over the standard giving the actual increment of growth. The tape 

 was thus merely used to transfer the circumference of the stem to 

 the standard length, and not to measure it. 



Ihe tape was kept in a dry room, and from November, 1918, to 

 April, 1919, 6 ft. 9 in. on the tape corresponded to 6 ft. 9 in. on 

 the standard. The tape then began to shorten, and most rapidly 

 during May, until 6 ft. 9_V ^^ ^^^ tape covered 6 ft. 9 in. on the 

 standard, and on June 15th, 6 ft. 9/^. By July 2nd the tape had 

 shortened a further ^V of an inch. A similar tape kept in a damp 



-cellar for a month shoi-tened J inch per 8ft. in this time, although 

 the temperature was fairly constant. The effect is, therefore, due 

 to the gradual absorption of moisture, the humidity of the air in- 

 creasing greatly in Melbourne during w^inter. 



The deepening of the girdle On the tree reduced the circumference 

 from 6 ft. 11^ in. to 6 ft. 8f in. 



In the previous year's measurements growth did not become per- 



•ceptible until the first week in November, but here it began during 

 the first week of October. This was the same time as when the 

 cambium began to divide in the previous years measurements, so 

 that the removal of the cork ring allows the actual growth to become 



•sooner perceptible externally. In 1918 growth ceased at the end of 

 February, but in 1919 it continued until the middle of March. 

 This was probably, however, the result of the exceptionally mild 

 and favourable autumn experienced in 1919. The total growth in 

 1917-1918 was IJ in., and in 1918-1919 U in. 



