88 



E. stellulata Sieb. — " I have seen bark of E. stellulata (which Mueller includes in 

 section 5), which cannot be distinguished from what are known as Ironbarks." (Maiden 

 in Proc. Linn. Soc, N.S.W., 1278, 1890, and Part V, p. 129, of the present work.) It 

 really belongs to the smooth-barks or Gums, and this Ironbark character is not strictly 

 typical. 



E. viminalis Labill. — Luehmann (Proc. A.A.A.S., vii, 524) quotes the remarkable 

 variation in the bark of E. viminalis in Victoria. He says : — 



This tree, which grows around the Melbourne herbarium building, shows here, in its sapling state, 

 a smooth, whitish bark, until it attains a diameter of from 4 to 6 inches, then gradually the outer layers 

 remain attached, at first near the base only, becoming rough and brown ; as the plant gets older, these 

 • layers creep higher and higher up the stem, until, in aged trees, the whole of the trunk and also the larger 

 branches are covered with a thick, rugged, dark brown bark. Within 10 miles inland from Melbourne, 

 already the tree changes its character in this respect, inasmuch as only the lower part of the stem is covered 

 with this rugged bark, while another 10 miles further towards the ranges this species presents a smooth 

 white trunk, except, perhaps, just near the ground. Although the floral characters remain the same, 

 yet anyone seeing only the two extreme forms would certainly consider them two distinct species." 



Mr. R. H. Cambage has taken a photograph to illustrate this. The bark of this 

 particular tree is the reverse of the normal White or Ribbony Gum, and it will be found 

 illustrated in due course. So, also, will an excellent photograph of a rough-barked 

 viminalis in Studley Park, Melbourne (Hardy). 



It has been found, in a number of cases, that trees with barks approximately 

 smooth, in low-lying situations, may become increasingly rougher or more fibrous-barked 

 in more elevated, better drained situations, such as hill-sides or tops of hills. Examples 

 are : — E. regnans (the rough-barked variety has been described as E. fastigata), E. saligna 

 and E. viminalis. 



5. BARK IN RELATION TO HEAT AND COLD. 



In connection with Mr. Cambage's observations, recorded at pp. 318-9, Part L, to 

 show how careful one has to be in interpreting the relation of the bark to resistance to 

 heat and cold, we find that those species which are exposed to the greatest extremes 

 in these directions are the smooth-barked (Leiophloiee), those which have a naked look. 

 A priori, one would expect the Stringybarks, with their blankety covering, to be most 

 cold or heat-resistant, just as we pack a tiree with a coat of straw or other non- 

 conducting material to pass it through an inclement winter. We adopt no corres- 

 ponding method in dealing with trees in relation to hot winds and high temperatures 

 generally, simply because it is not convenient to do so. 



Nature's method, as regards Eucalyptus in these situations, is not to employ 

 dead tissue for non-conducting purposes, but smooth, thick, parenchymatous tissue 

 full of water-containing cells, which offer considerable resistance to extremes and changes 

 in temperature. 



The thickness of bark varies considerably with the habitat, being greatest in deserts and other dry 

 situations and in alpine regions, and least in the tropical rain forest. Individuals of a species common to 

 two situations have the thicker bark in the more xerophytic habitat ; alpine and light cultures show more 

 bark than lowland and shade cultures. Probably in most cases thick bark is associated with high 

 transpiration, and thin bark with low transpiration. (Coulter, Barkes and Cowles, op. cit., ii, 707.) 



