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VII. Bevislon of the Suborder Mimosese. By George Bentham, Esq 



F.Jl,S, 



(Plates LXYI.-LXX.) 



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Bead June 18th, 1874. 



I 



HAVE witliin the last few years had occasion to lay before the Society some observa- 

 tions on two groups of plants which, however different in most respects, arc both of them 

 remarkably distinct in their circumscription, and as constantly uniform in those clia- 

 racters which it has been the custom to res^ard as the most essential. To the two micrht. 



indeed, have been assigned equal grades in the hierarchy of the Natural System, ^^Tre it 

 not for the enormous disproj)ortion in the number of their species. Upon abstract prin- 

 ciples. Cassia and CompositcB might equally well be treated as good genera ; both arc per- 

 fectly isolated; the pistil and seeds are uniform in each; the variations in the corolla are 

 scarcely more marked in the one than in the other ; the androecium and fruit present 

 perhaps more important diversities in Cassia than in Compositse : but Cassia has only 

 350 species, whilst Composita^ number 10,000. Cassia has therefore been universally 

 retained as a single one, or at most only three genera, whilst Compositse are variously 

 divided into from 750 to 1200 genera. I have now to offer a few remarks on a third 

 group, almost as definite in circumscription, and intermediate, as it were, between the two 

 as to uniformity and numbers. The 1200 Mimosese are as uniform in their pistil as the 

 350 Cassias and 10,000 Compositse ; the corolla is more uniform than in either ; the 

 androecium and fruit are, as in Cassia^ much more varied than in Compositaj. Like 

 Cassia, the MimoscEe were established by Linnaeus as a single genus ; and perhaps, if 

 Composita3 had not been so largely extratropical, and consequently presented .to his 

 observation in considerable numbers, if he had only known that proportion of tropical 

 forms which he possessed of the two other groups, he would probably have considered 

 them also as forming only one or three genera ; or, on the other hand, had not his 

 specimens of Mimose* been so very few and meagre, or fragmentary, he would probably, 

 from the first, have divided them into at least three genera. At the present day Cassia, 

 almost restricted constitutionally to the shrubby or arborescent plant-form and tropical 

 elimate, and even there not prospering as a race in all stations, has remained within 

 manageable limits as to numbers, and is stiU regarded as a smgle genus, divisible mto 

 three marked sections. Mimose*, which, with one great southern exception, have 

 remained constitutionally, as weU as geographically, withm nearly the same limits as 

 Cassia, have, however, nearly four times as many species, and are therefore admitted as 

 a suborder, divisible into three marked tribes and some twenty to thirty genera ; and 

 Composite with their prevalent herbaceous or low shrubby plant-form flouxishmg espe- 

 ciaUy in ex tratropical or mountain climes, shunning only low tropical fores lands, have 

 nearl thirty times the number of species of Cassia, and have accordingly been sub- 

 aii;^ cuniy Liiuc founded on characters which m Cassia and 



divided into innumerable genera, otten lounatu u 2 T 



VOL. XXX. 



