44 president's address. 



Here the flattening appears in ^ome cases entu-ely on the distal jjortions without 

 attecting the petiole, in othei-s both petiole and rhachis are involved to varied 

 extents. How these are to be interpreted under one general law seems incompre- 

 hensible." 



Preston does not say whether the seven leaves figured are such as are to be 

 found on ordinary plants, whose growth has not been interfered with by pruning 

 or othei'wise. In the absence of descriptions of the plants or of seedlings, and of 

 personal knowledge of the species, or of any other like it, I cannot settle the 

 point. But they are certainly comparable with some of the leaves of reversion- 

 shoots, as shown in my Plates, especially PI. iii.-vi. They are pictures of the 

 contest between the flattening common petioles, or leaf-axes, and the pairs of 

 pinna;. They illustrate very well the inversely proportional ratio in which the 

 two antagonists are present in any particular leaf; and how, if pinnae are present, 

 no matter where they may be located, the flattening of the leaf-axis is retarded 

 where they are situated ; and how, if they are absent on some part of the axis, no 

 matter where, the flattening of the axis is correspondingly favoured in that parti- 

 cular region. The localised damping or retarding effect of the presence of the 

 pinna? on the flattening of the leaf-axis is very well shown in some of his figures. 



But the idea that the so-called phyllodes of some Acacias are flattened petioles 

 which have lost their blades, and of others, that they are flattened axes which 

 have lost their pinnae, is erroneous. There are not two kinds of phyllodes. so- 

 oalled, of Acacias. The two hypotheses, that there are, cannot be harmonised. 

 Therefore. I am prepared to go further than Preston, and say that the attempt to 

 interpret them under one definite law not only seems, but is, incomprehensiltle, 

 inasmuch as it is not possible. The so-called phyllodes of Australian Acacias ai-e 

 not flattened petioles which have lost their blades, as both seedlings, when they are 

 correctly interpreted, and reversion-foliage and reversion-shoots demonstrate. 

 Therefore, they have been improperly called phyllodes; and consequently any 

 attempt to interpret them in terms of something which they are not. cannot b\it 

 be futile. But when it is realised that the euphyllodes of all the Acacias of which 

 we have sufficient knowledge, are flattened leaf-axes or common petioles, which 

 have lost their pinnae, then it becomes possible to say, that there is but one definite 

 law which applies to all that are known, and that it is a readily comprehensible 

 law. 



I regret that I am unable to consult Reinke's paper,* referred to by Preston. 

 It is not available in Sydney. The abstract of it in the Journal of- the Royal 

 Microscopical Society (1897, p. 549) does not include Reinke's views about 

 phyllodes. Under the circumstances, Preston supplies what one chiefly wants to 

 know, namely — "-1. ruhida A. Cunn. and .1. IteteroplniUa Willd., have aireaily 

 been described by Reinke, and in his article one stage in the transition as it 

 occurs in -I. helerophylla is figured. According to tliat author, the change is 

 merely a gradual flattening of the petiole, accompanied by the reduction of parts 

 more distal." It is not surprising that Preston was unable to reconcile tlie views 

 here stated, with the characteristics of the leaves which he figures. 



Goebel, in liis "Organogi'aphy of Plants" (Vol. i., p. 166, fig. 10'2 I remarks^ 

 "The best known and most frequently quoted are the species of Acacia which pro- 

 duce phyllodes. The phyllodes arise by the l)roadening in a vertical direction of 

 the leaf-stalk, sometimes also of the leaf-midrib, whilst the lamina aborts. Seed- 

 ling plants (Fig. 102). however, have, without exception, so far as they have been 

 examined, leaves which are like those of the species — possessing a bipinnate 



* Reinke, J., " TTntersuchnngen iiher die Assimilationsorgane der Ijeguminosen." 

 Pringrsheim's Jahrb. f. wiss. Bot. Brl. xxx., 1896. 



