L90 E. C. Andrews — The Geological History of the 



into existence. This may be placed tentatively in the later 

 ( Cetaceous. 



in Australia Acacia and its allies are represented by modi- 

 fications of the genus, as local subgenera or sections, which 

 have a general appearance very different from that of the world- 

 wide section Gummiferse. One of the Australian sections, 

 namely Phyllodinese, with about 420 species, is leafless, but 

 possessing a development of phyllodes remarkable for their 

 variety of form and structure. 



Vulgares, another great section, or subgenus, is plentiful 

 in Asia, Africa, and America, but is absent from Australia. 

 Another subgenus is endemic in Tropical America. 



No local genera grouped around Acacia occur in Australia, 

 but in America there is the vast genus Mimosa (400 species) 

 with a few outliers in the Old World. 



Cassia contains about 400 species and is divided into three 

 subgenera by Bentham 12 namely, Senna, Fistula, and Lasior- 

 liegma. All these subgenera show the same combination of 

 general characters in America, Asia, Africa, and Australia. 



Fistula has above 20 species, about 8 in America, about 5 in 

 Asia, 5 in Africa, and but 1 in Australia. These species are 

 local, forming natural combinations into intermediate groups. 



The great subgenus Senna, with more than 200 species, has a 

 similar wide distribution, excepting the section Psilorhegma, 

 which is confined to the Old World with its chief center in 

 Australia, but, as Bentham remarks, these Australian species 

 are truly Australian in type, namely, in their leaves being 

 rigid, vertical, terete, or in having phyllodia developed, and 

 with the pods straight or variously twisted. 



Lasiorhegma is world-wide in distribution, but the three 

 natural sections, Apoucouita, Absus, and Chamcecrista, into 

 which it is divided, are distributed differently. Apoucouita 

 consists of 3 or 4 American trees. Absus has 70 localized 

 American species and 1 type an annual, abundant in Tropical 

 Africa, Asia, and Australia, but not in America. 



Chamcecrista has many herbs and undershrubs with 50 to 

 60 species in America and from 16 to 20 in the Old World. 



Vernonia, a genus of about 500 species, and closely connected 

 with many small genera, "has its chief centers in tropical 

 America and tropical Africa, forming in both countries more 

 or less divergent groups, but in different directions, the species 

 more numerous in America, the forms more varied in Africa. 



12 Revision of the genus Cassia, Trans. Linn. Soc. London, vol. xxvii, pp. 

 503-513, 1809. 



