326 ISLAND LIFE 



nearly 3,000 fathoms deep, rise up to within a few hun- 

 dred fathoms of the surface, and seem to indicate the sub- 

 sidence of two islands, each about as large as Hawaii. 

 The plants of North Temperate affinity may be nearly as 

 old, but these may have been derived from Northern Asia 

 by way of Japan and the extensive line of shoals which 

 run north-westward from the Sandwich Islands, as shown 

 on our map. Those which exhibit Polynesian or Australian 

 affinities, consisting for the most part of less highly modi- 

 fied species, usually of the same genera, may have had 

 their origin at a later, though still somewhat remote 

 period, when large islands, indicated by the extensive 

 shoals to the south and south-west, offered facilities for the 

 transmission of plants from the tropical portions of the 

 Pacific Ocean. 



It is in the smaller and most woody islands in the 

 westerly portion of the group, especially in Kauai and 

 Oahu, that the greatest number and variety of plants are 

 found and the largest proportion of peculiar species and 

 genera. These are believed to form the oldest portion of 

 the group, the volcanic activity having ceased and allowed 

 a luxuriant vegetation more completely to cover the 

 islands, while in the larger and much newer islands of 

 Hawaii and Maui the surface is more barren and the 

 vegetation comparatively monotonous. Thus while twelve 

 of the arborescent Lobeliacese have been found on Hawaii 

 no less than seventeen occur on the much smaller Oahu, 

 which has even a genus of these plants confined 

 to it. 



It is interesting to note that while the non-peculiar 

 genera of flowering plants have little more than two 

 species to a genus, the endemic genera average six and 

 three-quarter species to a genus. These may be con- 

 sidered to represent the earliest immigrants which became 

 firmly established in the comparatively unoccupied islands, 

 and have gradually become modified into such complete 

 harmony with their new conditions that they have de- 

 veloped into many diverging forms adapting them to 

 different habitats. The following is a list of the peculiar 

 genera with the number of species in each. 



