24 president's address. 



it lias to do. Discussion tliereon would be promoted. If taken up and entered 

 into entliusiastically, tlie subject of drought-problems should become a live sub- 

 ject, as it ougbt to be, ami as it needs to be; and then we may expect to make 

 some progress. 



Next only to the need of righteousness, and of the maintenance of tlie in- 

 tegrity and welfare of the Empire, the question of how to cope successfully with 

 droughts in Australia, stands second to none in its importance. For Australia's 

 bid for greatness rests upon this, inasmuch as her agriculture and other possi- 

 bilities can only be imperfectly realised without it. 



(Kv TlIK CORRKCT I XTKRPKET.iTlOX OP TH !•; SO-CALLKU PhYI.LODES OF THE 

 AUSTRALIAX PhVI.LOUIXEOUS AcAt'IAS. 



(Plates i.-viii. ) 



The Australian Hora furnishes numerous examples of plant-structures, which, 

 as one usually sees them, are difficult to understand, jiartly because they repre- 

 sent secondary developments which have been superimposed on the primal y, 

 natural order of things; and partly because one commonly meets with complicated 

 adult structures, of which the early stages are not always readily obtainable. The 

 so-called phyllodes of Australian Acacias are one of the most common and 

 familiar examples of these plant-puzzles. These have been regarded as the 

 '•classical'' examples of phyllodes, because there are so many species of pliyllo- 

 dineous Acacias, and they are so widely distributed . Nevertheless, strictly sjieak- 

 ing. they are not "phyllodes" within the meaning of the recognised definition of 

 these leaf-substitutes. For example, in the Glossary of Terms prefixed to the 

 first volume of the Flora Australiensis (p. xxxix.) will be found the definition — 

 "Pli,\llodiuin - a flat petiole with no blade." Asa Gray defines a phyllodium as 

 "a petiole usurping the form and function of a leaf-blade." In both cases, these 

 definitions are intended to apply to the flattened leaf-suljstitutes of the Australian 

 phyllodineous Acacias.* Bentham says of Division i., PIn/llodiiieae — "Leaves all 

 (except on young seedlings and occasionally one or two on young branches') re- 

 duced to phtjllodia, that is to the petiole either terete or angular or more or less 

 vertically dilated so as to assume the appearance of a rigid simple leaf, with 

 an upper and a lower edge or margin, and two lateral simifar surfaces, and 

 either sessile or contracted at the base into a short petiole, the upper edge often 

 bearing 1, 2, or rarely 3 or more sliield-shaped or tubercular or depressed 

 glands." (Fl. Austr., ii.. p. 319.) 



But the so-called phyllodes of the Australian phyllodineous Acacias are not 

 simply Hattened petioles which have lost their blades. The current statements 

 about them, such as those f|uoted above, are imperfect generalisations based upon 

 inadequate material. On the contrary, they are the flattened, primary leaf-axes 

 or common petioles of bipinnate leaves which ha\e lost their iiinuiv; and it is 

 the fiirmer which have usurped the forui and I'unctiou of the latter; and not 

 fiatteneil petioles which have usurped the form and function of leaf-blades. 

 The so-called phyllodes of Au.stralian Acacias may be long, or short, or very 

 short. If long, they are the flattened primary axes, or common petioles, (.f 

 potentially long bipinnate leaves, with numerous pairs of lunnir. If short, or 

 very short, they are the flattened primary axes, or common petioles, of potentially 



•tiray's Botanical Text-book (18871. pp. 110. 426. 



