PRESIDENT S AHUDESS. 



bipiiinate leaves of Aeaeia-seedlings with only a single pair of theiu, which ap- 

 pear sueeessively after the first simply pinnate leaf, or in some cases after an 

 opposite pair of them, represent a pair of pinnae at the node immediately above 

 the leaf-stalk or petiole ? I have not yet met with any description of Acacia 

 seedlings or Acacias in which this question is answered, or even considered, 

 except by Preston, referred to later on . As a matter of fact, the pair of pinnae 

 of bipinnate leaves, with only one pair, such as successively make their appear- 

 ance after the first simply pinnate leaf, or a paii- of them, represents the 

 apical pair; and what is below them is the entire primary leaf -axis or common 

 petiole, and not simply the ordinary petiole. That is to say, the succession 

 of the pairs of pinna? in the development of a bipinnate leaf with several pairs 

 cf pinnae, of an Australian Acacia, is basipetal: and not basifugal, as tacitly 

 assumed, and taken for gi-anted. 



It is interesting to note, therefore, how two eminent liiologists, like von 

 Mueller and Lubbock, independently came to the conclusion that, not merely the 

 same sort of evidence, but the selfsame evidence — the evidence afforded by the 

 "first leaves" of phyllodineous Acacia-seedlings — demonstrated and proved two 

 divergent, and irreconcilable hypotheses: the metamorphosis of liipinnate leaves 

 into phyllodes by the confluence of leaflets, stalklets and stalks in the one case; 

 and by the flattening of the petioles and the disappearance of the blades, in the 

 other. AVhat is wrong with these two discordant conclusions is not that one is 

 correct, and the other incorrect; but that neither of them is wholly correct, and 

 that both are partially iucoiTect. Mueller's hypothesis is incorrect in so far as 

 the leaflets and stalklets, that is the pinnae, are concerned ; for these abort entirely, 

 and take no part whatever in the formation of the so-called phyllodes. The 

 e^'idence on that point is clear and conclusive; and one is at a loss to under- 

 stand how Morren and he were led to think that the leaflets and stalklets con- 

 cresced with the stalks or axes. But the stalks, that is the primary axes, or 

 common petioles of the actual or potential bipinnate leaves, the ordinary petioles 

 together with the rhachises, do flatten to form the so-called phyllodes, and are 

 the only components thereof; and, to that extent, his hypothesis is correct. But 

 Fupposing that there is a confluence of leaflets, stalklets and stalks, why was 

 Mueller content to call such structures phyllodes, when, by the current definition, 

 phyllodes are flattened petioles, which have lost their blades — neither more nor 

 less? 



On the other hand, Lubbock's hypothesis is incorrect in supposing that, in 

 the formation of Acacia phyllodes, so called, "nothing remains except the flat- 

 tened petiole"; whereas, in truth, everything remains except the iiinn*. But 

 it is correct in so far as the pinnae are concerned, for these vanish entirely. 



T\'hile lack of adequate material, and of personal knowledge of the plants 

 as they grow under natural conditions, are the ultimate reasons for the long- 

 standing, incorrect, current ideas about the phyllodes, so-called, of Australian 

 Acacias, there ai-e three main proximate reasons : — 



(1) The ambiguous, because too general, statements about the "first leaves" 

 of the seedlings of the Australian phyllodineous Acacias ; and the neglect to deter- 

 mine the mode of the succession of the pairs of pinnae in the development of the 

 bipinnate leaves. 



(2) Either the non-recognition of the jiresence of tlie "seta teriiiiiialis" of 

 Bentham, or "the recurved point," or the "excurrent point" of the common petiole 

 or of its distal component, the rhachis; or, if noticed pnd mentioned, the disre- 



