46 THE TRANSEVRSE SECTIONS OF PETIOLES OP EUCALYPTS 



As to the fibro-vascixlar system, it is observed that aggregation of the bundles 

 generally occurs in woody plants, as we found to be the case, and that bicollateral 

 bmidles occur in the Myrtaceae, among others. In the genus Eucalyptus, at any rate, 

 the bundles are concentric. 



However, the importance of the structure of the petiole for taxonomic purposes is 

 clearly established in this paper, and he naturally insists on the importance of the 

 petiole for purposes of classification. 



A few of the facts recorded in the various suggestive and instructive papers on the 

 Eucalyptsby J. Bosisto, Esq., C.M.G., read at different periods before this Society,* 

 may be noticed in connection with our present subject. He is led to the important 

 conclusion that the volatile oil is the base of other products, such as resin-like 

 substances, inasmuch as those species, great in the production of the oil, vigorously 

 supply it to the atmosphere, and thus do not allow sufficient time for the formation 

 of resinoid bodies, which require the absorption of oxygen by the leaf; and, 

 conversely, those species less vigorous in oil production allow time for such a 

 purpose, and so become well stored. 



This suggested to us that there might be some relation between the size and 

 number of cortical cavities, and the greater or less production of oil or resinoid 

 bodies respectively. Two of the chief oil-producing species are amygdalina and 

 globuhis, and of kino-producing species, leucoxylon and rostrata. On referring to 

 the detailed description, amygdalina is found to have the smallest and fewest 

 cavities of any of these, being even surpassed by viminalis, which yields the least oil. 

 Globulus has certainly large and moderately numerous cavities, but, on the other 

 hand, leucoxylon is not far behind it, which yields kiuo to the extent of even 22 per 

 cent, from fresh bark. 



We have observed that as a rule the notable producers of oil do not show 

 numerous cortical cavities in their petioles, so that we may perhaps conclude that the 

 production of kino in the leaf-stalk is not immediately dependent on the production 

 of oil in the leaf-blade. It is in the leaf-blade alone that the oil is manufactured, as it 

 was proved to be absent from the petiole, so that, contradictory as it may appear, it is 

 in the leaf-blade, with its two surfaces equally exposed to sun and air, that the least 

 oxidised constituent— the volatile oil— is made. To prove the absence of oil from 

 the leaf-stalk (at least in amygdalina, and presumably in the others), a simple 

 experiment was made, which may be briefly described. 



Branchlets of fresh leaves were kindly supplied by Mr. Slater, of Mitcham 

 Grove, such as he is in the habit of using for distilling his well-known oil. The 

 largest and best leaves were selected, and 1000 petioles, carefully snipped off' and 



* See Trans, and Proceedings of Roy. Soc. of Vict., Vol. XII., &e. 



