36 • president's address. 



Seventy-eight years ago, Mr. Bentbam monographed the species of Mimosa. 

 He began his paper by formulating some definitions." Thus he said — "Before 

 entering into descriptive details, some preliminary explanations may be necessary 

 relating to some of the terms used in characterising Mimoseoe, and applied by 

 different writers in different senses. ... I have uniformly adopted the 

 phraseology usually followed by De Candollc, giving the name of pinnae to the 

 primary divisions, and of foliola to the ultimate divisions [of the bipinnate leaf]. 

 I have also designated by petiolus communis, the xi-hole of the stalk 

 to which the pinnae are affixed, not (as is done by Kunth), that part only which 

 is below the lowest pair of pinnae, and by petiolus partialis I have meant the 

 whole of the stalk to which the foliola are attached." Accordingly, in this paper, 

 Bentham refrains altogether from using the terms petiole and rhacbis. 



The adoption of the term common petiole, in the sense defined, has the ad- 

 vantage of avoiding a possible difficulty — namely, if the portion of the common 

 petiole of a bipinnate leaf below the lowest pair of pinnae, the petiole in the 

 Kuuthian sense, is longer than the internode immediately above, how is one to be 

 cjuite sure that at least one pair of pinnse, below the lowest pair present, has not 

 been suppressed; and that, consequently, the supposed petiole is only ap- 

 parently, and not really, the actual petiole? 



When Bentham came to deal with the Acacias in the second volume of the 

 Mora Austrabensis (18G4), he adopted a somewhat different and mixed termin- 

 ology, partlj- as defined above for the Mimoseae proper, and partly in accordance 

 with the definitions given in the Introduction and Glossary prefixed to the de- 

 scriptive matter in the first volume. While stiU using the term common petiole 

 for the whole of the stalk to which the pinnae are affixed, he also uses the term 

 petiole, in the Kunthian sense, for that part which is below the lowest pah- of 

 pinucB; and he also uses the term rhachis. But I do not understand Bentham to 

 use the term common petiole as synonymous with the term rhacliis. as defined in 

 the Introduction- — "39. The common stalk [of a compound leaf] upon which the 

 leaflets are inserted is called the common petiole or the rhachis." 



If one examines the impari-pinnate leaves of Tecoma capensis (4 pairs), 

 T. radieans (4-5 pairs), Rohinia pseudacacia (8 pairs), Ailanthus glanduhi!<a 

 (up to 14 or more pairs) — all common garden-plants, with leaves of the same 

 type, varying considerably in length according to the number of the pairs of 

 leaflets, with fairly large leaflets, much about the same breadth — it may be 

 noticed: (1) that the length of the intemodes corresponds to, or is a little longer 

 "than the greatest breadth of the leaflets, so that these may be fully exposed to the 

 light without any overlapping; (2) that the leaflets are fairly at right angles to 

 the axis to which they are attached; (3) that by the leng-thening of the petiole of 

 the terminal leaflet, this also is fairly displayed without overlapping the leaflets 

 of the pair next below; and (4), that the petioles — the portions of the common 

 petioles below the lowest pair of pinnje — are relatively short or very short, no 

 longer sometimes than the lowest internode, or half as long again, or a little 

 longer . 



If, next, one examines the pari-pinnate leaves of Cassia C andolleana. also 

 common in gardens, with four pairs of leaflets, it may be noticed: — (1) that the 

 intemodes are about as long as, or a little longer than, the greatest width of the 

 leaflets; (2) that, in the absence of the terminal leaflet, the leaflets of the first 

 pair, or of the first and second pairs next below, usually move slightly inwards, 



• Bentham, "Notes on Mimoseae, with a short Synopsis of Species." Hooker's Journal 

 of Botany, Vol. iv., p. 342, 1842, 



