2 go SCIENCE PROGRESS. 



are transported by oceanic currents, birds, and winds, with- 

 out destroying their vitality. In another article I pro- 

 pose discussing these agents of dispersal in some detail. 

 The absence from the above list of the two largest natural 

 orders — Leguminosae and Compositse — may cause some 

 surprise, especially as the seeds of many of the former bear 

 long immersion in salt water with impunity, and the pappose 

 achenes of the latter are often, it is assumed, conveved 

 lont{ distances bv wind. Le^uminos£e are rare in all 

 oceanic islands, both coral and volcanic ; but Composite, 

 on the other hand, are characteristic of many volcanic 

 islands, the Galapagos and St. Helena, for example. 



The distribution of the plants of the Tonga or Friendly 

 Islands has been worked out by the writer (5), and a few 

 of the most interesting facts may be repeated here. This 

 group lies to the south-east of Fiji, between 18 and 23 

 south latitude, and 173 and 176° west longitude, and com- 

 prises both volcanic and coral islands ; some of the former 

 being considerably larger than those of the Gilbert Group, 

 and rise to altitudes of 500 to 3000 feet. Fuller informa- 

 tion on the geology of the islands will be found in an article 

 (6) by Mr. J. J. Lister. But although the Tonga Islands 

 are considerably larger than the Gilbert Islands, it is more 

 in land area and altitude than external dimensions, and 

 it is due partly to the absence of central lagoons. Ton- 

 gatabu in the south, the largest of the group, is about 

 twenty-two miles in its greatest length, and is composed 

 entirely of coral limestone. This island is the best known 

 botanically ; but Mr. ]. J. Lister, whose collections were 

 worked out for my paper referred to above, thoroughly ex- 

 plored the neighbouring smaller, though more elevated, 

 Eua, which gave a considerable number of additional 

 species. Since the publication of my paper, Kew has 

 acquired a collection of dried plants made by Mr. C. S. 

 Crosby in the Vavau cluster in the north. This collection 

 has not yet been thoroughly worked out, but although 

 it doubtless contains some additions, they will not be of a 

 character to modify what has been written respecting the 

 affinities of the flora of the whole group. The total num- 



