﻿340 MR. G. BENTHAM ON THE MIMOSE^E 



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carpa it appears to be vaguely defined or variable, depending perhaps in some measure 

 on soil and weather. The articulation is less decided in the thick fleshy or hard pods of 

 a few species of Fithecolobmm, both from the Old and the New World, and of Acacia 

 concinna, and in the flat pod of Alhizzia stipulafa, several of which species have been 

 proposed as genera solely on account of this articulation. In Entada and JPlathymenia 

 it is limited to the endocarp, from which the valves fall away with the margin in Flat- 

 hymenia, usually without it in JEntada. 



The twisting of the valves after dehiscence of many species of Fifhecolobium and of 

 the common Adenantheray the development of a spongy or pithlike endocarp of Frosopis, 

 the central longitudinal wings or angles on the valves of Tetrapleura and Gagnebina, the 

 woody texture of the valves of Xylia, are all very secondary characters, more or less 

 distinctly exemplified in scattered species of the very natural genus Acacia. 



Of the nature and origin of the " pulp " which has been supposed to characterize the 

 pods of Inga^ Fithecolobium, Frosopis, StrypJinodendroUy BichrostachySy Acacia farne- 

 siana, &c., I can find no good account ; and it is very difficult to form an opinion from 

 dried specimens. In most cases it appears to be a development of, or an exudation 

 from, the endocarp or inner layer of the substance of the pericarp ; in Inga it is described 

 as a " pulpy arillus," which the dried fruits do not enable me to verify. In most, 

 perhaps in all, species of the section Unguis- cati of FithecoloUum, the funicle is dilated 

 into a fleshy arillus, often half enveloping the seed, but of a very different aspect from 

 that of the remains of dried pulp often adhering to the seeds of Inga, That any real 

 development of the funicle, however constant in the above-mentioned section of Fithe- 

 colobiim, is not generally of much beyond specific importance in Mimosese, is evidenced 

 by the extraordinary variety in the forms of the funicle in the Australian Acacice, noted 

 in the specific descriptions in my Elora Australiensis. 



In considering the systematic value of the characters by which the different Mimosese 

 are to be distinguished, it is further necessary to take into account how far they may 

 have been affected by geographical distribution. In this respect I need not here refer to 

 such plant-forms as the arborescent, the herbaceous, the scandent and others, in respect 

 of which the Mimosese afford no data different from those derived from plants generally, 

 and which have been worked out by Grisebach, in as far as dependent on external 

 physical conditions only ; but there are a few others which may require a short mention, 

 as resulting in some measure from genealogy, acting independently of or in combination 

 with physical and other causes. 



The phyllodineous development of the common petiole of the leaves, with a total 

 arrest of the pmnse and leaflets in aU but the seedling and first foUowing leaves, is an 

 essentially AustraHan character, and yet cannot well be attributed to physical influences. 

 It extends equally over the whole territory in its varied climates, spreading sparingly to 



the islands of the Pacific, but is limited in the Mimeses of these regions to the single 

 genus Acacia. It is exemplified, however, in no less than 270 Australian species. There 

 are no traces of the tendency in Asia or in Africa. In South America it reappears in a 

 slight degree, but affecting a different group of the suborder. Two Brasilian species of 

 IBmosa and an extratropical one of Frosopis, as also, if I was correct in the deter- 



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