Dec.,"] 

 1912 J 



Kelly, Concerning Acacia Phyllodes. 115 



CONCERNING ACACIA PHYLLODES. 

 By Reginald Kelly. 



{Read before the Field Naturalists' Club of Victoria, 14th Oct., 1912.) 



Leaves, according to Dendy and Lucas, pp. 147-8 — to use 

 a reference easily available — are lateral outgrowths from the 

 stem or branch, specially modified and adapted organs for 

 purposes there .detailed. Their tissues are continuous with the 

 corresponding structures of the stem. " A leaf of the most 

 s])ecialized type consists of a flat expansion — the blade or 

 lamina — which is attached to the stem by a narrow stalk or 

 petiole. . . . There is no distinct mark of separation in 

 young leaves between the stem and the petiole or between the 

 petiole and the lamina. The stem rises up into the petiole, 

 and the petiole widens out into the lamina. In some older 

 leaves transverse layers of cells are formed, which delinitely 

 mark off these regions from one another. The transverse 

 layer of cells is called an articulation or joint, and the leaf is 

 said to be articulated. The i)etiole ultimately becomes 

 articulated to the stem in all deciduous stalked leaves, and the 

 blade, or its parts, arc articulated to the petiole in such leaves 

 as those of the orange, the ash, and the acacia. . . . The 

 amount of differentiation of the petiole and lamina is by no 

 means the same in all plants. In the orange a broad petiole 

 bears a broader lamina, separated from it by an articulation ; 

 both parts of the leaf are here blade-like. In many of the 

 acacias the petiole is broad and blade-like, and only bears a 

 lamina in the seedling plant. In a full-grown shrub or tree 

 the broad petioles are alone produced ; these perform all the 

 functions of leaves, and are termed phyllodes. The ])hyllodc 

 can l)e recognized as a petiole and not a leaf by comparing its 

 structure with that of the undoubted petiole in the seedling 

 leaves : the arrangement of the fascicular bundles in parallel 

 veins is the same in both." 



Is it, then, a fair deduction from that authority that the 

 practicable discernible difference between true leaves and 

 phyllodes lies in the arrangement of the fascicular bundles, and 

 whether they are in parallel veins or reticular or branched 

 from a midril) (which, after all, is only a glorified vein), there 

 seems so little difference as almost to force the conclusion that 

 the parallel-veined leaves of the monocotyledons are not true 

 leaves, but phyllodes. The real difference between leaves and 

 phyllodes, I think, is to be found in the history of their 

 structure, and it is with this that I propose mainly to deal. 



Acacias as we now find them have — 



(a) Ijijiinnate leaves in both the adult and the ju\rnile 

 states, as illustrated by the dccurrcns grou]) ; or 



