Over a South Atlantic Continent 439 



also Pittosporiim and Vitex deserve to be emphasized, not 

 only in themselves, but in their frequent relation as host- 

 plants for members of the mistleto family or Loranthaceae. 

 All three genera, in the species they contain, and in the 

 present geographical distribution of these, probably were 

 of East Asiatic origin, and though Metrosideros is absent 

 from Australia, its near ally Callistemon is abundant there. 

 Either by the Afro-Indian or the Australian-Tasmanian 

 passage-way these must have reached the Southern Conti- 

 nent and there spread profusely. But further, during the 

 migrational period, they acted as hosts for* species of 

 Loranthiis , that are quite incapable of growing on the 

 ground. So whether we regard the coeval passage of Lor- 

 anthiis along with its host plant as having been effected by 

 the one bridge or other indicated above, the necessity for 

 a continuous land passageway is strongly indicated. 



But if a wide southern continent once stretched from 

 W. Patagonia eastward to N, Zealand and the Kermadec 

 Islands, one would expect, on the basis of all present evo- 

 lutionary evidence, that specific variations would often 

 occur, and that these variations would in turn start new or 

 incipient species and even genera, that would become in not 

 a few cases geographically isolated, owing to constant 

 changes in the configuration of land and water. Both 

 results are strikingly true. 



Thus J. D. Hooker, in his N. Zealand and Tasmanian 

 floras, also subsequent writers on the flora of Patagonia, 

 of Tristan, of Kerguelen, of N. Zealand, and of Tasmania, 

 often refer to the marked variability of species described, 

 or confess the difficulty they have experienced in referring 

 a certain plant to one species or to another previously 

 named. And again each of the geographic regions men- 

 tioned, possesses species and even genera peculiar to itself, 

 or to a restricted geographic area. Thus Pringlea anti- 

 scorhiitica, Acaena affinis and Colobanthus kerguelensis are 

 confined to the Marion, Crozet, Heard and Kerguelen 

 groups, or to one or more of them; Aciphylla, Nothothlaspi, 

 Hectorella, Hoheria, Entelia, Alectryon, Corynocarpus, and 

 Carmichaelia are genera of the Australasian area; Pen- 



