CH. Ill] FLORA OF NEW ZEALAND. 127 



unable to withstand the higher temperature of the surface 

 waters in the tropics can pass in safety. 



This view however mav be too elaborate ; besides it 



mf 



should apply also to the Serolidse which are considered 

 below 1 ; another suggestion may arise from the habits 

 of these Crustaceans ; the Serolidse live at the bottom and 

 swim and crawl on the sand ; the Arcturidae on the other 

 hand are stated to cling with their hinder thoracic limbs 

 to any available object ; in this way they might easily 

 happen to select some floating piece of wood which would 

 ultimately take them on a voyage to the more northern 

 from the more southern regions. 



An analogous series of facts with perhaps an analogous 

 explanation is offered by the flora of New Zealand. There 

 are many resemblances in the flora of New Zealand to 

 that of Europe. Mr Wallace says that " one-third of the 

 entire number of New Zealand genera (115) are found 

 also in Europe, and even fifty-eight species are identical 

 in these remote parts of the world." No doubt it is easier 

 for many plants than for many animals to cross wide 

 tracts of ocean, but Mr Wallace is of opinion that mountain 

 ranges offer a convenient mode of transit which has been 

 probably made use of. The difficulties of a change of 

 temperature would be in this way overcome ; as a matter 

 of fact European plants are known from intermediately 

 lying mountain tracts such as the Himalayas. 



1 In the Chapter dealing with the Antarctic continent. 



