presidext's address. 35 



piiuife are represented by large leaflets, some of them with serrated edges. I 

 have also other leaves showing more advanced, but still, incomplete transforma- 

 tions. On the other hand, one can get examples in which the terminal pinna is 

 jH-esent, Ijut the leaHets are not expanded. In this condition, it is apt to be 

 fugacious; and one often tinds only a withered or broken remnant of it. The 

 basifugal succession of both the pinna! and the leaflets in the development of the 

 bipinnate leaves is vei-y interesting. The pinna in the basal region are usually 

 short; in the middle region they are very long, with numerous pairs of pinnae, and 

 s tei-minal leaflet. The internodes may be as long as, or shorter than the spread 

 of an opposite pair of expanded leaflets. The petiole is relatively very short, 

 as long as about two or three, or more, internodes, if some of the possible lowest 

 pinna' do not develop. The variable length of mature leaves on the same plant, 

 that is the variable number of the pairs of pinnae present, is, I think, attributable 

 to accidents, at different stages of gi-owth, to the apical portion of the leaves 

 before the basifugal development of the full number of pinnae is complete. 



The leaves of CalUandra have up to six or seven pairs of pimiffi. As in the 

 bipinnate Acacias, the terminal pinna, as well as the terminal leaflet of the pinnae, 

 has been arrested; but, in Iwth cases, their remnants, the terminal seta3, are pre- 

 sent, unless accidentally missing, and are esjieciully noticeable in young leaves. 

 Of a leaf with six pairs of pinnae, the length of the common petiole was 34 inches; 

 Ihe spread of a pair of opposite expanded leaflets 11, or about the length 

 of two internodes; and the length of the petiole 2-1. The petioles of these 

 leaves, proportionately to the length of the common petioles, are the longest I 

 have met w^th; and the length of the internodes is less than the spread of an 

 opposite pair of leaflets ; but this causes no overlapping .as the apical pair of 

 pinnie, and one or two pairs below them move upwards and inwards, and the 

 basal pair move downwards and inwards. 



The youngest leaves of .1. discolor that one can get, siiow excellently the ter- 

 minal setae both of the common petiole and of the pinnae (PI. viii., fig. 2). Also 

 that there is no addition of pinnae at the apex of the leaf, after the lowest pinna? 

 are developed, as in Jacaranda. All the pinnae that are to be present in the mature 

 leaf, are represented in the primordium of the leaf; and when the pinucP of the 

 young leaves move into place, and the leaflets expand, the iiinnfe are all equally 

 developed . Similar statements are applicable to the very young leaves of A. 

 decurrens. 



Fig. 2 of PI. iii., shows the leaf of a seedling of this speciei*, with three pairs 

 of pinnae, the middle pair of which illustrate the incomplete ba-sipetal development 

 of the leaflets. 



Due recognition of the meaning and significance of the terminal setcB of the 

 leaves of the bipinnate Acacias, and especially of the leaves of seedling's with 

 only one pair of pinnae, is the key to the understanding of euphyllodes. What- 

 ever else may be wanting, the apical pair of pinnae- is always present, unless acci- 

 dentally missing, except in decadent stages such as are shown in Plate vii. 



The Petioles or the Lea\'es of Bipinx"ate Australiax Acacias 



The euphyllodes of some Australian Acacias are very long, from 12-20 inches. 

 In considering the nature of such remarkable developments as these, it is neces- 

 sary to consider some of the characters of the leaves of the bipinnate Acacias. 

 and especially of their petioles. 



