CH. ll 



INTRODUCTORY 



The next chapter gives a few ilhistrations of the successful 

 manner in which Age and Area has been applied to the making 

 of predictions about local distribution. For example, the floras 

 of the outlying islands of New Zealand being in general derived 

 from the same sources as that of the main islands, must be com- 

 posed of species that were among the earliest arrivals, in their 

 own affinity groups, in New Zealand, and should therefore by 

 hypothesis, be very widespread there. This proved to be the 

 case, in a very striking manner, the species of the islands ranging 

 on the average nearly 300 miles farther in New Zealand than the 

 species that did not reach the islands. Further, the endemic 

 species that reached the islands ranged much farther in New 

 Zealand than the widely distributed species of New Zealand that 

 did not reach them. This result seems explicable only by aid of 

 Age and Area. Other predictions that were equally successful 

 are also instanced, and it will suffice to say that as Age and 

 Area has been applied in this manner in over ninety cases with- 

 out a failure, the hypothesis now stands upon a very firm basis. 

 A further chapter is then given to the consideration of the 

 way in which it may be applied to the study of the invasions of 

 plants that may have reached a country, New Zealand being 

 taken as an example. By a consideration of an imaginary case 

 in which a single widely distributed species enters New Zealand 

 and gives rise to endemics in a casual way, it is shown that the 

 endemics in a country will in general show numbers decreasing 

 from the centre where the parent entered down to the two ends. 

 On examining the facts it was found that all the genera of the 

 New Zealand flora gave such curNxs. A study of the position of 

 the maxima shows that they are concentrated in three chief 

 regions— north, south, and central— and one infers that these 

 must have been the centres of corresponding invasions. Careful 

 study of the curves given by the single invasions goes to show 

 that the northern was much older than the southern, and this 

 is confirmed by the fact that the latter is mainly composed of 

 the more mobile group of herbs, while the former is chiefly trees. 

 Lastly, Chapter ix is devoted to a detailed consideration of 

 the many objections that have been brought >ip against Age 

 and Area, and many or most of them seem to be satisfactorily 

 met, very many of them depending simply on misunderstanding 

 of the work upon which it is based. 



