97 



There are many references to this twist in European, and some in American 

 literature, but few in Australian. One of them is the following, and I invite attention 

 of country observers to the problem, premising that their observations will have 

 permanent value if they collect twigs of the trees observed, in order that their specific 

 identity may be ascertained. I may refer to this Torsion or Twist in Bark and Timber 

 under Meteorology later. 



Dr. (J. B.) Cleland contributed a " Note on Twists in the Bark of the Jarrah (Eucalyptus marginatg 

 Sm.)." Of one hundred trees observed in the neighbourhood of Perth, Western Australia, four showed a 

 decided left twist, sixteen a slight left twist, forty-four were straight, twenty-four showed a slight right 

 twist, nine a marked right twist, and in three the twist was undecided (i.e., irregular). As there 

 appeared to be no indication of a tendency to tree-growth in a spiral direction, the explanation was offered 

 that, when young, a predominant branch probably extended to one or other side, and, being played on by 

 the prevailing wind, caused the young stem to become twisted to some extent. Later such a branch may 

 have died and disappeared. The explanation offered seems to be favoured by the fact that contiguous 

 trees are often twisted in opposite directions. (Proc. Linn. Soc. N.S.W., xxxiii, 291, 1908.) 



The twist of the bark of E. gigantea is decidedly to the left. See the photo, in 

 my " Forest Flora of New South Wales," vol. vi. 



Speaking of the bark of a Gum, Professor A. J. Ewart writes to me, inculcating 

 caution in observation : — 



Re twist in Eucalyptus globulus, I have not made any special observations, but doubt whether 

 the appearance is not largely an optical effect, as in a climbing plant. In stems which appear twisted 

 the fibres may cross one another in opposite directions, and their inclination is not that of the apparently 

 twisted stem. 



But Gums (e.g., E. tereticornis), however, do show twist in a marked manner, 

 and I hope that some observer will systematically take the matter up, as far as Australia 

 is concerned. 



Mr. J. F. Campbell, the well-known New £outh Wales surveyor, writes :— 



The Eucalypts, as far as I have observed, do not conform to any fixed mode of development as 

 regards their growth curvatures. Spiral twisting is least noticeable within the dense stands of timber 

 or in the brush areas, but the trees which skirt these areas are usually twisted and frequently gnarled. 

 Thinly scattered timber almost invariably show well-defined growth curvature (owing to the lack of 

 shelter from the wind, J.H.M.). The cross-grained character of the Eucalypt is readily seen when logs 

 are split radially. The split surfaces show both dextrorse and sinistrorse growth curvatures alternating 

 irregularly. 



My non-Australian references shall be of the briefest. 



1. Schlich, v. 39, says :-— " . . . it is found that those (trees) twisting from left to right (against 

 the sun's apparent course) are harder to split than those twisting in the opposite direction." (He is, of 

 course, referring to the northern hemisphere.) 



2. It is also, of course, the direction of the apparent movement of the sun in the northern 

 hemisphere. Some writers (e.g., the Belgian geologist, Van den Broeck) say that the twisted trunks of 

 trees are produced by the earth's rotation, and therefore when they exhibit a spiral they should show a 

 right-hand spiral in the northern hemisphere, and a left hand in the southern, like the turn of the cyclonic 

 storms or the twist in water vortices; but this is still open to more exact observation. It has also been 

 suggested that, as the winds due to the earth's motion blow fairly steadily just when the trees are growing 

 fast, the young trees may take a permanent twist from this cause, which it never loses. (" The Curves 

 of Life," by T. A. Cook, p. 31.) 



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