323 



The following tables ^^^ will make this clear : — 



Approximate area in 

 Orchid Flora of square kilometres. 



1. Australia 



2. New Guinea 



3. Java 



4. Tropical Africa 



5. Brazil 

 British India 

 Central America 

 Japan and Liukiu Islands 

 Philippines 



Orchid Flora of 



1. 



2. 

 3. 

 4. 



5. 

 6. 

 7. 



Australia 



New Guinea 



Java 



Tropical Africa 



Brazil 



British India . 



Central America 



8. Japan 



9. Philippines 

 In instituting such comparisons. 



Total number 

 of species. 



7,700,000 circa. 450 



786,000 2,205 



126,000 600 



6,000.000 750 



8,468,950 1,850 



4.809,100 1,500 



2,400,000 2,000 



382,300 147 



300,400 723 



Average number of 



square kilometres to 



each species. 



17,111 



356 



210 

 8,000 

 4,579 

 3,206 

 1,200 

 2,600 



415 



is necessary to take into consideration 

 the very large unoccupied central area of the continent, which Sir Joseph 

 Hooker ^-^ estimated as two-thirds of the total superficies, and which he believed 

 to be incapable of bearing vegetation on account of its arid character. In the 

 light of modern knowledge, it is now known that this area is by no means un- 

 productive for many forms of plant-life, but that owing to its low rainfall and 

 absence of large waterways, it does not carry an orchid-flora. Consequently 

 Hooker's statement still remains approximately true so far as this type of vege- 

 tation is concerned. 



Due allowance, therefore, having been made for this fact, the fertility of the 

 orchid-bearing areas may be roughly estimated at 5,700 square kilometres per 

 species, a result which is comparable to that of Brazil, a tropical country rather 

 larger than our own. 



2. Flora of Exotic Origin. 



So far as it has been investigated, the orchid-flora of tropical Australia bears 

 a very close relationship with that of Southern Asia, and particularly to that of 

 the Malay Peninsula and New Guinea. 



From North-western Australia, only three orchids have so far been reported. 

 The three genera to which they belong are to be found in Asia ; one of the species 

 also occurs in New Guinea and another is sectionally represented there. 



The Northern Territory has disclosed up to the present only 12 genera and 

 22 species. Eleven of the former are to be found in the Malay Archipelago or 

 in New Guinea; in those places also five of the species occur and others have 

 sectional representation. 



The same thing happens in the case of tropical Queensland, where out of 53 

 genera no less than 41 are in common with New Guinea or the Archipelago, and 

 usually with both stations. 



(1) Adapted from Schlechter's "Orchidaceen von Deutsch-Neu-Guinea," p. xv. 



(2) "Flora Tasmaniae, Introductory Essay," p. xxx. 



