•206 Ewart and Tovey : 



.the 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 api^reciably 

 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 



vthat slight variations in circumference Avere shown fi'om 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 was 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- 



jnent Astronomer, on the stone basement. After each measurement 

 with a waxed tape it was extended over tlie 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 measui-e it. 



Ihe tape was kept in a dry room, and frt)m Novendx?r, 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 on the tape covered 6 ft. 9 in. on the 

 standard, and on June IHth, 6 ft. 9y''^. 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 ^ 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- 



kCreasing greatly in Melbourne during winter. 



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 tlie first week in November, but here it began during 

 the first week of Octolier. This was the same time as wlien 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, ]>ut in 1919 it continued until the middle of March. 



'This w-as probably, however, the result of the exceptionally mild 

 and favouiable autumn expeiienced in 1919. The total growth in 

 1917-1918 was 11 in., and in 1918-1919 U in. 



