316 

 Texture. 



Their texture is very variable. In all the species there is a certain firmness, but with some, this 

 firmness makes them exceptionally coriaceous. (Naudin, 2nd Mem., 10.) 



Mr. E. H. Cambage is one of the few botanists who has written on the 

 subject : — 



The thickening of the epidermis for the purpose of sheltering the stomata, is one of the expedients 

 resorted to by the Eucalypts to resist evaporation, and consequently it is compatible with such an 

 endeavour, that those species having the thickest epidermis and of which such as E. dumqsa may be taken 

 as a type, are commonest in the interior. But this particular character is to be met with intermittently 

 in all the four climatic divisions of New South Wales, so that it would appear that various species have 

 adopted this precaution for preservative objects but from different causes. A dwarfed Port Jackson form 

 of E. capiteUata has remarkably thick almost orbicular leaves, while large normal type specimens within 

 a few miles have lanceolate foliage of ordinary thickness. The thick-leaved form, however, grows in the 

 more exposed positions, and in the more rocky situations with probably less plant-food available. It 

 seems. therefore not improbable that in order to counteract the effect of strong winds, to which its exposure 

 renders it liable, and also to compensate in some way for the limited nourishment it obtains, that the 

 thick-leaved adaptation has been evolved in this case, to preserve the starch which forms in the leaf and 

 which is regarded as an auxiliary food supply.. It is of interest to note that the thickest leaved types 

 usually correspond with the more dwarfed forms, and when the same species at maturity occurs both as 

 large and as stunted trees, it is on the latter that the thickest leaves are found. 



Turning next to the Eucalypts in the cold climate, wc find a similar variation in leaf characters. 

 The foliage of E. Gunnii as dwarfed trees on Mount Roland in Tasmania at nearly 4,000 feet above sea- 

 level, is distinctly thicker in texture than that of the same species around Guildford Junction at an 

 altitude of 2 ; 000 feet, and where the trees are upwards of 80 feet high. 



The leaves of E. coriacea are always somewhat leathery, as the specific name would imply, but in 

 observing trees of this species from just above the 2,000-feet level around Goulburn upwards to the 6,000 

 feet level towards Kosciusko, it is found that with the ascent the leaves get gradually smaller and thicker., 

 and the trees become dwarfed from the rigid conditions and weight of winter snow, until at last they appear 

 as gnarled shrubs with interlacing branches and the now thickened leaves have been reduced in length 

 from about 6 to 3 inches. 



It therefore appears that the sub-arid conditions of the inland country, and the coldest effects of 

 the mountains, though extreme in their climatic influence, have so operated in regard to this particular 

 phase of leaf character as to bring about the same result. It is suggested, however, that the modifications 

 of the internal structure of the leaves of two Eucalypts which originated before the Kosciusko uplift, and 

 developed until the present time under those two extremes of climatic influence, would not be the same, 

 and, although the leaves of E. coriacea at 6,000 feet have their counterpart in the interior at 500 feet, so 

 far as the thickening character is concerned, yet in their venation they are distinct from those of all species 

 found in that dry region. (Proc. Roy. Soc. N.S.W., xlvii, 36, 1913.) 



I quite agree with Mr. Cambage that thickness in leaves is sometimes evidence 

 of lack of transpiration. The thickest leaf in Eucalyptus known to me is E. tetraptera 

 (and to a less extent E. Preissiana). Both of these are denizens of a coastal region 

 in south-western Australia, east of a well-watered belt. The saline Avinds (tending to 

 xerophytic conditions) and a moderate rainfall, combine to induce this thickness of 

 tissue. E. incrassata var. angulosa, very common near the sea in Western and South 

 Australia, may be even succulent in texture. To mention other species which love 

 the saline breezes would be to enumerate^ those with abnormally thick leaves. Thus 

 we have E. capiteUata. E. dbtusiflora, and many others. 



