﻿650 MR. G. BENTHAM ON THE MIMOSE.E. 



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woody valves, are entirely vsrithout the pith or pulp ; and in no case can the nature of 

 the pod be safely guessed at from the examination of a flowering specimen. 



Plates LXIX. and LXX. represent some of the pods of a series as natural as that of the 

 Fhyllodinece, the Gummiferce, of which the majority are African but are also represented 

 in Asia and America. Among these, A.farnesiana (PL LXIX.) has been frequently pro- 

 posed as a distinct genus, under the names of Vachellia, Farnesia andAldina, on account 

 of the seeds, although at first normally arranged, becoming, as the pod advances towards 

 maturity, irregularly imbedded in a pithy substance filling the turgid pod. A similar 

 arrangement will be observed in A. giraffce; and the pithy substance, although with a 

 more regular arrangement of the seeds, is developed in A . macracantha and a few others, 

 all of which agree also in the little annular bract under the flower-head being at the 

 summit of the peduncle, instead of in the middle or lower down. This, however, appears 

 quite insufficient to constitute a genus when there is nothing to distinguish it in habit, 

 foliage, inflorescence, flowers, or seeds ; for the pods of ^. macracantha show an approach 

 to those of A. arabica (erroneously placed by Grisebach in VachelUa, for they are not 



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pithy between the seeds) ; the pithy substance occurs in many Australian FhyllodinecB 

 without any corresponding differences. It would be, moreover, very unnatural to place 

 in two different genera A. giraffes and A. heheclada (figured immediately under it), two 

 species very similar in every respect, even in the thick, turgid, oblong pod, merely on 

 account of the pith, abundant in the one and absent in the other. 



Por the A, macracantha, with turgid pods pithy inside, and A, arabica, with flat, 

 though thickly coriaceous pods continuous inside, I have figured several specimens, 

 showing the gradation from the deeply indented to the straight-edged forms observable 

 in both species, differences which have induced many botanists to distinguish two species 

 in the A. arabica; but in the numerous specimens I have now seen from various parts 

 of the wide area of the species, I have observed several intermediates between any two of 

 the four forms figured, and in one borrowed specimen, returned before these plates were 

 drawn, one half of the pod was deeply indented and the other half quite continuous. 

 The pod of ^. macracantha varies, moreover, from flat to almost cylindrical— in the 

 former case, however, usually dried before it is fully ripe. 



In Plate LXX. the first three pods of the upper half have their valves thick and some- 

 what succulent, so that A. albida, seen without the flowers, has been moi 

 taken for a Trosopis with exceptionally exalbuminous seeds. In the loi^^r half the 

 pods of ^. latromm and A, abyssinica are quite flat, but coriaceous • in 



than 



,. ^, , . coriaceous; in ^.cZ«%em and 



A. nubica the valves are convex ; m A. ebumea from India, and A. comtricta from Texas 

 the pods closely resemble those of a large proportion of Australian JPhyllodinecB 



I have not figui-ed any bf the Acacice Vulgares ; for the pods are much more uniform 

 generally flat and straight, sometimes Uke those of Alhizzia, but usually not so broad 

 more conaceous and more readily dehiscent, and often undistinguishable from those 

 of P^ptaden^a, of which the flowers are so different. The exalbuminous seeds readily dis- 

 tmgmsh them from the otherwise similar fruits of Zeuccena 



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