BOTANICAL AND CHEMICAL CHARACTERS OP EUCALYPTS. 101 



in some Eucalypts, this is formed in such quantity that at times as 

 much as one-sixth of the air-dried bark consists of crystallised calcium 

 oxalate (4), showing plentifully a fomi of twinning in geniculate crystals. 

 The tannin stored in the barks of these oxalic acid forming species is 

 of good quality for tanning purposes and affords a very good tanning 

 extract; it might be profitable, therefore, to work some of these barks 

 for this material — oxalic acid could then be obtained in quantity, as a 

 by-product, from the residues. E. salubris, of Western Australia, is a 

 species which might be so worked. The chemistry and botanical 

 features of E. sahibris show it to be closely associated with the class 

 of Eucalypts known as ' Mallees,' trees which form the short stunted 

 vegetation or ' Mallee Scrub ' extending over much of Australia. In 

 these ' Mallee ' species lime is a dominant mineral constituent and 

 they all form oxalic acid in abundance, the one factor, perhaps, being 

 the corollary of the other. It is hardly to be expected that species which 

 produce oxalic acid in abundance would live long enough to form very 

 large trees, so that the tendency to develop a shrub form may have been 

 brought about through adverse chemical influences operating in these 

 groups; and it is interesting to find magnesium in such quantity in 

 the ashes of Eucalyptus which reach a very large size, particularly as 

 such trees only store mineral matter in their timbers to the extent of 

 about one pound to 2,000 pounds of anhydrous wood. It is thus seen 

 that the amount of any element is small, the CaO representing in 

 E. regnans about one 15,000th part of the weight of the moisture-free 

 timber and the MgO about one 10,000th part. 



Essential Oils. — The essential oils of the numerous Eucalyptus 

 species vary in composition in a striking degree but the variation is of 

 a remarkably uniform character (5) and apparently has been contem- 

 poraneous with distinctive botanical changes; this is strongly brought 

 out by the progressive alteration in the veins of the mature lanceolate 

 leaves (6), starting from the featherlike venation of the members of 

 the Corymbosce group, through the intermediate form representative 

 of the members of the cineol-pinene group, to the looping or butterfly- 

 wing venation of the leaves of the ' Peppermints ' and the 'Ashes,' a 

 form indicative of the presence of the terpene phellandrene. These 

 three types of leaves are shown in the accompanying Plate V. : — 



The varying thicknesses of the midribs : the disposition of the 

 marginal veins ; the second vein in No. 3 ; and the varying amount of oil- 

 glands in these pictures should all be noted. 



The first type is represented by the Angophoras and by certain 

 Eucalypts, between which there is general chemical agreement. The 

 terpene in the oils of the species of Eucalyptus characterised by this 

 venation and also in the Angophoras is pinene ; phellandrene does not 

 occur in them and cineol is either absent or only present in small 

 amount, whilst the yield of oil is always small. The second type of 

 venation is characteristic of the species which yield oils consisting of 

 pinene and cineol ; the oils richest in cineol are obtained from leaves 

 having this venation; it is well shown in sucTi species as E. globulus, 

 E. Bridgesiana, E. goniocalyx, E. Smithii, &c. Oils derived from 

 species with this venation do not contain phellandrene; as the lateral 



