642 



SCIENCE 



[N. S. Vol. XLV. No. 1173 



species under average conditions. It is as- 

 sumed that the forms, common to both islands, 

 arrived or originated there before this sepa- 

 ration arose. 



On any theory some endemic species will 

 be older and others younger. The first may 

 now occupy the whole country, but the latter 

 only parts and the youngest even only small 

 parts of it. Climate and environmental con- 

 ditions are so uniform throughout the islands 

 that on the theory of natural selection no part 

 of them has a greater chance of producing 

 endemics than others and an equal distribu- 

 tion should be expected. The actual facts, 

 however, contradict this conclusion and show 

 that the endemics with a small distribution 

 are heaped up in the center of the coimtry, 

 whereas toward the north and south they be- 

 come regularly rarer. The endemics found in 

 the extreme ends are almost only those which 

 occupy the whole or a great part of the range. 



This most interesting law of distribution is 

 proven by a series of tables, which elucidate 

 it from different sides and by means of differ- 

 ent statistical arrangements. It clearly points 

 to some cause which is independent of the uni- 

 form climatic conditions, and also of the spe- 

 cial adaptability of the species. It holds for 

 the species of the families and larger general 

 as well as for the whole flora, and for those 

 occurring also outside of the islands as well as 

 for those confined to them. In other words, it 

 governs the distribution of the forms, which 

 originally reached New Zealand from elsewhere 

 and first populated it, as well as that of the 

 native types. 



The explanation proposed is this: Wew Zea- 

 land is separated from the nearest land area of 

 important size by an immense stretch of water, 

 and so it is evident that few species can have 

 arrived there in recent times, apart from the 

 influence of man. The species of foreign 

 origin, i. e., of wider distribution, or the 

 " wides " as Willis calls them in opposition to 

 the endemics, must therefore mostly be very 

 old and widely spread all over the islands. 

 This latter fact is borne out by the statistical 

 tables. Now the soundings show, that the 

 shallowest water approaches ISTew Zealand to- 



wards the center of the chain of islands. On 

 the view that this place was its last connection 

 with a larger continent, sunk beneath the sea 

 in geological times, we may assume it to be 

 the point from which the spreading of the 

 main part of its present angiospermous flora 

 has begun. 



As the wides spread slowly from this center 

 toward the extreme northern and southern 

 parts they must have produced new forms from 

 time to time. The oldest of these may have 

 spread along with them, and now occupy the 

 whole area. The younger forms, however, did 

 not find, as yet, the time to do so; they must 

 still be local forms. About three quarters of 

 the wides, but only one third of the endemics 

 are now found to occupy more than half the 

 length of the chain of islands and this fact 

 shows clearly that the endemics are not better 

 adapted for distribution in New Zealand than 

 the wides. 



On the other hand, there are only 30 wides 

 of very local occurrence, i. e., occupying less 

 than 160 miles or 1/6 part of the whole length 

 (1,000 miles), whereas about one third of all 

 the endemics or 296 species are in this condi- 

 tion. It is obvious that for some reason or 

 other the wides could spread, whilst the en- 

 demics could not. No theory of adaptation 

 can explain this phenomenon, but it is very 

 simply understood on the ground of Willis's 

 law that the local species are the youngest, 

 and have not, as yet, had the time to secure a 

 wider dispersal on the islands. 



I must refrain from dealing with the con- 

 tents of all the twelve tables and with the dis- 

 cussions of their results. But from the facts 

 adduced it seems evident that the theory of 

 natural selection can not explain the distribu- 

 tion of the angiospermous species of New 

 Zealand, and that this distribution clearly 

 points to some general cause, which must be 

 the same for all families and all arbitrarily 

 chosen groups of plants as well as for the flora 

 of all different countries. The theory of " age 

 and area " seems the only one broad enough 

 to comply with these requirements. 



Hugo de Vbies 

 LuNTEREN, Holland 



