2 THE TRANSVERSE SECTIONS OF PETIOLES OF EUCALYPTS 



Perhaps one result of this investigation will be to direct attention to the 

 distinctive nature of the tissues of the leaf in other groups of plants as well as the 

 Eucalypts. This has already been done, for instance, in the Gnetaceae and Coniferae 

 by Dr. C. E. Bertrand* and Prof. M'Nab.f The latter confined his attention to the 

 Coniferae, and, in addition to the general anatomic structure of the transverse section 

 of the leaf, noted the distribution and number of the resin-canals, and the arrange- 

 ment of stomata on the surface, as aids in his diagnosis. 



While we have likewise described and drawn the transverse section as a whole, and 

 found the total characteristics of the section of any species to be of great value for 

 identification, there are certain features very useful for that purpose, even when 

 taken alone. Thus, the cortical cavities, whether many or few, large or small ; the 

 size and shape of the section ; the relative thickness of the epidermis, &c.; but it is 

 the woody-tissue forming characteristic figures which is the most striking part. 

 This wood-pattern is fairly constant for each, so that the most enduring part of the 

 entire section fortunately gives a clue to the affinity sought for. 



It would appear that even from an economic standpoint some reliable means 

 are much needed for determining a given species of Eucalypt, from a readily accessible 

 portion of the plant, such as the leaf. It is highly desirable, in the interests of 

 trade, not to speak of science, that one species should not be confounded with 

 another, for the timber has such specific variations that serious loss and mischief 

 might in many cases ensue. 



Mr. Maiden, of the Technological Museum, Sydney, in his recently published 

 work on the " Useful Plants of Australia," writes on this subject, at p. 427, in very 

 decided terms : — " Scarcely a branch of Australian economic botany is in a more 

 confused state than that which pertains to the timber of the Eucalypts. The genus 

 is, perhaps, the most difficult one in the world, intrinsically, and also because of 

 accidental circumstances, i.e., difficulty of obtaining flowers and fruit, and irregular 

 flowering seasons ; moreover, the trees vary, according to climate and soil, to such 

 an extent as to render a definition of the species rather expansive, and, as this 

 difficulty often extends to the wood, timbers of totally different character are 

 sometimes reckoned under the same species." 



Such a state of matters calls for some remedy, and it is evident that the present 

 investigation tends in that direction. The leaves being evergreen are a constant, 

 and not an accidental circumstance. The deep-seated characters revealed by the 

 section are not so variable as others more dependent on soil and climate ; and a 

 definition which is included in, and shown by, the transverse section of a petiole, 

 can hardly be called expansive. 



* Anatomie Comparee des Tiges et des Feuilles chez les Gnetacees et les Coniteres. Paris, 1874. 

 t Pioc. Roy. Irish Acad., Series II., Vol. II., 1875-77. Remarks on the Structure of the Leaves of certain Coniferae, 

 and a Revision of the Species of Abies. 



