AKTICLE I. — The Teansverse Sections or Petioles of Eucalypts as aids in 

 THE Determination of Species, by D. McAlpine, F.C.S., and J. E. Eemfry. 

 (With Plates 1, 2, 3, 4, 5, and 6.) 



(Read Thursday, November 14th, 1889.) 



I. — Introductory, 



The Eucalypts form such a prominent feature in the Australian vegetation, and 

 have such varied uses, that any addition to our knowledge of their characters is sure 

 to be vi^elcomed. 



The primary object of the present paper is to show how transverse sections of 

 the petioles of Eucalypts may be used as valuable aids in the determination of 

 species. Sections of thirty different kinds are here described and photographed, and 

 they show unmistakably, along with a general resemblance, differences which are 

 more or less constant, and readily recognisable for each species. 



Anatomical characters of the leaf have already been successfully used in the 

 discrimination of species belonging to other divisions of the vegetable kingdom.* 

 Of course such characters, depending on a single organ, and apart from the aggregate 

 of characters, are apt to be more or less artificial ; but, when we consider that the 

 parts shown in transverse section of the petiole are in organic connection with, and 

 form an essential portion of, the vital machinery of the plant, it need not excite 

 surprise that they should vary in the different species, and be, to a certain extent, 

 characteristic for each. 



We know that the leaf is simply a lateral expansion or extension of the stem or 

 branch, usually bearing a bud in its axil, and its tissues are, as a rule, continuous 

 with those of the stem, so that in it we have an epitome of the parts concerned in 

 vegetative life — a point deserving of special notice in this connection. Besides, the 

 petiole, with which we are more particularly concerned, is capable of reproducing 

 the entire plant from a small portion of it, as in the well-known instance of the 

 ipecacuanha plant. The vegetative organs which, in some form or another, are 

 absolutely necessary for the life of the individual, have been too little used in the 

 discrimination of genera and species, while the reproductive organs have been too 

 often almost exclusively relied upon. The anatomist (dealing with internal structure) 

 and the systematist (often entirely occupied with external characters) must combine 

 their results in order to arrive at a proper conception of the true system of nature. 



* See De Bary, Comp. Anat. of Phanerogams and Ferns, p. 298. 



