148 A NATURALIST IN THE PACIFIC chap. 



sea-level ; but here is living under uncongenial conditions, and, like 

 Myoporum sandwicense, becomes dwarfed and shrubby. The 

 climatic conditions under which S. chrysophylla thrives in the 

 Hawaiian mountains are therefore those of the temperate zone. 

 From the data given in Chapter XIX., the mean annual tempera- 

 ture at an elevation of 6,000 to 7,000 feet would probably be about 

 55°, the average temperature of New Zealand. 



We must therefore look to the temperate and not to the 

 tropical zone for the home of the parent species of Sophora 

 chrysophylla ; and if it was originally derived from a shore-plant 

 dispersed by the currents, the widespread S. tomentosa could 

 scarcely have been the species concerned. But this strand-plant is 

 disqualified for another potent reason, since it belongs to a 

 different section of the genus. Whilst S. tomentosa belongs to 

 the section possessing smooth pods, S. chrysophylla is referred to 

 the section Edwardsia having four-winged pods, which comprises 

 about ten species found in Chile and Peru, Hawaii, New Zealand, 

 Further India, and the Isle of Bourbon. What strange principle 

 in distribution, we may fitly ask, has linked together in this 

 odd fashion the continents of the Old and New World and the 

 islands of the Indian and Pacific oceans ? 



Yet, discredited as Sophora tomentosa is as a possible parent of 

 the Hawaiian mountain species, it may yet afford us a clue. It is 

 significant that the distribution of this wide-ranging beach-shrub in 

 the tropics of the southern hemisphere is almost coterminous with 

 that of Sophora tetraptera, a species widely spread in the south 

 temperate zone from Chile to New Zealand and extending towards 

 the tropics as far as Juan Fernandez in lat. 33° S. and to Easter 

 Island in lat. 27° S. Though not strictly a beach-plant, S. tetra- 

 ptera is a plant of the sea-border ; and it is remarkable, but not 

 surprising, how in New Zealand, one of its principal homes, its 

 behaviour in respect of its vertical distribution presents a great 

 contrast to that of S. chrysophylla in the tropical latitudes of 

 Hawaii. We have seen that, in Hawaii, S. chrysophylla, which 

 thrives as a tree 20 to 30 feet high in the mountains, becomes 

 shrubby when it descends to the lower levels. In New Zealand, 

 S. tetraptera is, as we learn from Kirk, a prostrate shrub in the 

 mountains, whilst in the lower elevations towards the sea it 

 becomes a tree 30 and even 50 feet in height. It can scarcely 

 be doubted that, if we exchanged the habitats of these Hawaiian 

 and New Zealand species, each would to a great extent take up 

 the other's station and the other's habit. 



