254 THE VOYAGE OF H.M.S. CHALLENGER. 



Zealand species of Azorella, formerly regarded as constituting an independent genus 

 (Pozoa), differ in habit rather than structure from the typical Azorella. Much more 

 mioht be said in elucidation of this subject, but we must leave it here. The exploration 

 of the lofty mountains of New Guinea may be expected to throw some light on the former 

 distribution of southern types of vegetation. As an illustration of the southern type 

 extending northward in both hemispheres the genus Nertera may be mentioned. In the 

 Tristan da Cunha group, besides an endemic species, the very widely-dispersed Nertera 

 depressa occurs. This species is common in New Zealand and some of the neighbouring 

 islands, and South Australia, as well as in America, from Fuegia through the Andes to 

 Mexico, and also in some of the Pacific Islands. In New Zealand there are three other 

 species of the genus, two of which are endemic, and the third " appears to be also a Philip- 

 pine Island plant." There is one endemic Australian species, and two or three occur in 

 the mountains of Java and other islands of the Indian Archipelago, one of them being 

 closely allied to Nertera depressa. 



In conclusion, allusion may be made to the affinities of the flora of Marion, the Crozets, 

 Kerguelen and Heard Islands on the one hand, with that of the Tristan da Cunha group 

 and the islands of Amsterdam and St Paul on the other hand. Only two of the flowering 

 plants are common to the northern and southern groups of islands, namely, Ranunculus 

 biternatus and Uncinia compacta ; and the genus Accena is represented by different species 

 in these two latitudinal regions. Altogether, the vegetation of the northern group of 

 islands is of a type characteristic of a warmer climate, comprising American, New Zealand, 

 and African elements, associated with a proportionately large endemic one. 



