268 MORPHOLOGY OF ANGIOSPERMS 



Myrtaceae in South America and Australia, etc. This pairing 

 is still more evident if closely related families are included, as 

 the Sarraceniaceae in North America and the Nepenthaceae in 

 tropical eastern Asia and the East Indies. The pairing of 

 Australia and Africa is less notable, as the Mimosa tribe, massed 

 in tropical Australia and Africa, and the Thymelaeaceae, chiefly 

 occurring in temperate Australia and the Cape region. The 

 pairing of America and Africa, or the Atlantic-distribution, 

 is quite rare. 



7. The predominance of the American tropics in the devel- 

 opment of Archichlamydeae is marked, as might be inferred 

 from the last paragraph, almost all of the tropical groups being 

 represented there, and two great families (Cactaceae and Melas- 

 tomaceae) being almost exclusively American. 



8. As might be expected, there is a much greater display of 

 Archichlamydeae in the north temperate regions than in the 

 south. Two large families, however, are characteristic of the 

 south temperate regions namely, the Proteaceae, chiefly Aus- 

 tralian, some South African, and a few South American ; and 

 the Thymelaeaceae, characteristic of Australia and the Cape 

 region. 



9. It is of interest to note that the dominant tree-groups, 

 so characteristic of Archichlamydeae, are of different alliances 

 in the different regions. For example, in north temperate re- 

 gions the Juglandales, Fagales, etc., dominate; in the tropics 

 the Lauraceae are the characteristic tree-forms ; while in south 

 temperate regions the Proteaceae are the prominent archi- 

 chlamydeous forest trees. 



10. There is a notable diffusion of types into all regions, 

 so that very few families are restricted in their representation, 

 although most of them have a fairly definite region of massing. 

 Characteristic tropical families have representatives in the tem- 

 perate regions, and families chiefly developed in the temperate 

 regions have tropical representatives. 



SYMPETALAE 



The alliances of Sympetalae are comparatively so few and 

 well defined that they may be considered separately. 



EKICALES. This alliance is peculiar in containing distinct- 

 ly temperate and boreal forms. It includes an arctic family 



