Ivi PROCEEDINGS OF THE 



Australia and a vast extent of land including more or less of both 

 of Wallace's divisions of the Archipelago, How far subsequent 

 changes which have influenced the present distribution of animals 

 may have affected that of the forest vegetation can only be judged 

 of when the floras of Borneo, Celebes, and New Guinea shall have 

 been as well investigated and compared as have been those of 

 Sumatra and Java. 



Tropical Africa, or Grisebach's Soudan, is, as a botanical region, 

 separated from the Mediterranean region by the Sahara desert, and, 

 southward, from the Cape region by the dry district north of the 

 Gariep, termed by him the Kalahari, Geologists have expressed 

 their belief that this continent has subsisted as land from the most 

 remote antiquity. The large semiaquatic or singularly formed ter- 

 restrial animals, the very distinct bird-races, the varied connexions 

 of its entomology may all tend to support the hypothesis ; and many 

 of the peculiarities of its vegetation, as far as known, appear to 

 derive from it a plausible explanation, Grisebach, however, believes 

 that these peculiarities are entirely independent of the geological 

 history of Africa. He begins by remarking on the poverty of the 

 flora of Soudan, especially when compared with that of other tropical 

 regions of large extent, such as Brazil and tropical Asia — and this 

 notwithstanding the wide dispersion over the region of certain genera 

 and species, and, on the other hand, the indications of several special 

 centres of vegetation within it. But these centres of vegetation, he 

 says, have been very sparse in their productions, as well in the low- 

 lands as in the mountains. He observes that, if the long duration of 

 a continental existence from the earliest periods had any influence, 

 it is difficult to conceive why single districts should have enjoyed 

 such great advantages over others ; arid it is equally in contradiction 

 to any ideas of a multiplication of organisms through the lapse of 

 long periods, or of the expulsion of a more varied ancient vegetation 

 by foreign invasions, when we see that most of the families of plants 

 are so poor in their component parts, whilst Gramineae are so extra- 

 ordinarily rich. If there had been any force in action causing the 

 flora of tropical Africa to be transformed in one direction or another, 

 how could it have dealt with different groups with effects so opposite ? 

 " The more irregular," he adds, " the distribution and mode of 

 operation of centres of vegetation appear to us, the more humble 

 must remain our attempts at explanation, in face of the mysteries of 

 the productive force, which does indeed suit that which it does 

 bring forth to physical conditions, but does not actually call into 

 being all that is susceptible of life." (Vol. ii. pp, 141, 142.) 



