c^-yui] INVASIONS 83 



Summary 

 The application of the hypothesis to a study of the way in 

 which a country has been peopled by invasions of plants is 

 Illustrated by the case of New Zealand. If a species enter the 

 country and give rise casually to new (endemic) species, then, 

 If the country be divided into equal zones, it will generally occur 

 that the endemic species occupy the zones in numbers increasing 

 from tlie outer margins to some point near the centre at which 

 the parent entered. Applying this prediction to New Zealand 

 It was found that all the genera in the flora showed figures of 

 this type. Further, it was noticed that the points at which the 

 maxima occurred were not scattered casually all over the coun- 

 try, but tended to mass together in three places— northern, 

 southern, and central. The most reasonable explanation of this 

 is that these points represent the centres of correspondin<T inva- 

 sions. Curves are given showing the way in which both^wides 

 and endemics fall off, from the centres of the invasions, the latter 

 much the more rapidly. As the curves of the southern invasion 

 are much more steep than those of the northern, one mav perhaps 

 infer that the latter was much the older (perhaps even a geo- 

 logical period older), and this is confirmed by the fact that it 

 consists mainly of trees, while the southern is composed chiefly 

 ot herbs, and also by other considerations. It is clear that 4cTe 

 and Area can be applied with effect in the studv of the peopling 

 of a country with plants. 



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