28 presidext's address 



r 



gard of its meaiiiiiy: aiu! siguificaiife. when discussing tho nature aiul iiitcrpret- 

 tion of Acaeia-pbyllodes, so-called. 



And (3) The omission to take into account the siiiiiilc but very significant 

 fact, that the ])etioles, or apparent petioles of all the known Australian bipinnate 

 Acacias, of which twenty-two species are described by Benthaui in the Flora 

 Australicnsis, are short or even very short, relatively to the leugfh of the entire, 

 primary leaf-axes, or common petioles; whereas some Acacia-phyllodes, so- 

 called, are not only much longer than the petioles of any existing bipinnate 

 Australian Acacia, being as long as 12 to 20 inches in some species ; but are even 

 longer than the couunon petioles of the longest leaves of any known, bipinnate, 

 Australian Acacia. 



I propose, therefore, to consider these three questions seriatim, and in .some 

 detail, because it is time the real nature of the so-called phyllodes of Australian 

 Acacias was recognised and taken into account. The current belief about them 

 is a barren conception, which has obstructed the progress of knowledge, and 

 leads one into the wilderness. If the so-called phyllodes of Australian Acacias 

 are simi)ly flattened petioles which have lost their blades, there is nothing more' 

 to be said al)out them that is of any importance. But when one knows what 

 they really are, it is a simple matter to reconstruct the euphyllodineous 

 Acacias, and, then having done this, to find corresponding analogues among the 

 existing, bipinnate species. And not only so, but when one knows where, when, 

 and how to look for reversion-foliage and reversion-shoots of the right sort, one 

 can find Nature actually reconstructing them, as T sliall presently show. Having 

 arrived at this stage, the study of the euphyllodineous Acacias takes on an en- 

 tirely new, and extremely interesting and )iromising aspect. 



Thk "First Lkaves" of the Seedlings of ArsTRALiAX Acacias. 



From the extracts given above, it is eviilent that, by the expression the "first 

 leaves'" of Acacia-seedlings, Mueller and Lubltuck mean — and the same remark 

 will apply to other authors who express themselves similarly — the earUest leaves 

 which successively develop on young seedlings; and that neither of them takes 

 account of the simply pinnate leaf, or sometimes a i^air of opposite, simply 

 pinnate leaves, which is, or which are, actually the fii'st to appear. 



The foliage of the young' seedlings of the Bipinnata- is similar to that of 

 other plants with bipinnate foliage, in that the earliest leaves to make their 

 appearance are of a simpler type than those ^\•luch follow them in later stages 

 of the development of the complete hipiMnatc' leaf. Tlie march of progi'ess, as 

 is usual, is from simple to complex. 



The very first leaf is an abruptly pinnate leaf, with sevei-al pairs of leaflets, 

 or there may lie an opposite pair of them. The second is an abruptly bipinnate 

 leaf witii oiu' pair of pinn;p and more or less numerous pairs of leaflets. Now 

 this leaf, and others like it. which follow, represents and corresponds to a leaf 

 like the first, in which the ajiical pair of leaflets has been replaced liy an apical 

 pair of pinna;; while the lower pair, or pairs, of leaflets, counting from above, 

 have been suppressed. That tiiis is the correct view to take is shown by the 

 presence of the seta terminalia, or terminal seta, in which the primary leaf-axis 

 lerminntes in l)oth cases. Tliis is the renuiant of a terminal leaflet in the flrst, 

 al)ruptly pinnate leaf; and the remnant of a terminal pinna in the .abi-uptly bi- 

 pinnate second leal', and in others like it. as will be discussed more in detail 

 later on. 



