president's address. 41 



struggle between them. The potentially heavyweight euphyllodes knoek-out the 

 bantam pinnje very promptly in weak seedlings. But, in reversion-shoots, with 

 a weU-established root-system to back them up, they put up a much better fight, 

 and are able to prolong the strugglel, hopeless though it is. 



These specimens are most interesting because the euphyllodes are so long, up 

 to about 9 inches, and yet not too narrow. This means that, if they were not 

 euphyllodes, they would be bipiunate leaves with numerous pairs of pinniB, up to 

 15-20. Therefore, they contrast admirably with, and supplement the two cases, 

 one with very short and the other with euphyllodes of medium length, already con- 

 sidered. Nevertheless, they show only another phase of the same kind of thing. 

 The three ^re not special cases, but only those of which I have been able to get 

 adequate material. 



The illustrations (Plates ii.-vii.) need little explanation, if it is kept in 

 mind : — 



(1) That the succession of the pinna?, in the development of the compound, 

 bipinnate leaves of the Australian Acacias is basipetal, not basifugal, as 

 in the leaves of Jacaranda. In seedlings, the first leaf, or a pair of 

 them, is simply pinnate, a simpler type of those which come after it. 

 Then follows an abruptly bijtinnate leaf with one pair of pinnae, repre- 

 senting the replacement of the apical pair of leaflets of the first pinnate 

 leaf, without any representatives of the other pairs of leaflets. That it 

 is the apical pair, is shown by the presence of the terminal seta at the 

 apex of the common petiole of every leaf, from start to finish, unless it 

 is accidentally missing. Then, in due course, in the seedlings of the 

 Bipinnatae, of some of the EujjhyllodineaB, and in reversion-foliage and 

 reversion-shoots of any of them, follow leaves with two. three, or more 

 up to the complete number, or approximating thereto. These represent 

 always the apical pair and one, two, three, or more pairs, as the case 

 may be, up to the full number, of successive pairs of pinnse, in order 

 next below the apical pair. The apical pair is always present in every 

 leaf, however many pairs of pinnje may be present, except in the de- 

 cadent stages of the outgoing pinnae, as illustrated in Plate vii. 



(2) Therefore, if the full possible number is not present, the shortage is in 

 the lower portion of the series. Also, the good, well-developed pinnae, if 

 all of tliem are not equally well-developed, when a number of pairs are 

 present, are those attached to the upper jiart of the common petiole ; and 

 the poor specimens, sometimes only represented by leaflets, are attaciied 

 to the lower part of the leaf-axis, as is shown in figs. 1-4 of PI. vi., and 

 figs. 4 and 6 of PI. vii . 



(3) This provides an opening for the flattening of the axis to make a start 

 on tlie proximal portion of the leaf-axis, where pinnae are absent or 

 poorly developed. If only one pair of pinnae is present at the apex, the 

 surviving apical pair, as shown by the presence of the terminal seta, the 



entire leaf-axis may flatten from top to bottom (PI. iii., fig. 5; PI. vii.. 

 fig. 4) . Illustrations of flattening axes with an apical pair of pinnae, 

 more or less resembling my examples, are commonly shown in textbooks, 

 as confirmation of the statement, that the so-called phyllodes of Acacias 

 are flattened petioles which have lost their blades! 

 The figures of Plates iv.-v., and fig. 5 of PI. vi., show a few pairs (2-5) of 

 strong pinnae attached to the upper part of the leaf-axis ; well-marked flattening 

 of the axis in the lower part; but retarded flattening where the pinn» are situated. 



