AGE AND AREA 



[PT. I 



We may even take the genera, and consider those represented 

 by most species in a coimtry to be the oldest in the country. 

 Testing this on the flora of Stewart Island, we get: 



Thus, just as with the families, the proportion of genera 

 represented in Stewart shows a steady increase with the in- 

 creasing number of species in the genus from 20 per cent, of 

 those with one up to 100 per cent, of those with more than 

 20 species. 



If we test the same question on the farther outlying islands 

 of New Zealand, the Kermadecs, Chathams. and Aucklands. we 

 find that the average size of a family that reaches all three 

 groups is 47 species, of a family reaching only two is 14, reaching 

 one 5, and of a family reaching none is only 2. A similar result 

 follows a test of the genera. This fact also shows in the flora of 

 the islands off the British coast mentioned above. 



Or again, as the wides are, according to hypothesis, the oldest 

 forms, one will expect to find them the best represented in the 

 floras of the outlying islands of New Zealand. In New Zealand 

 itself the wides form about 18 per cent, of the flora in number 

 of species, but when we pass over into Stewart Island, the plants 

 reaching which must, by hypothesis, be older on the average 

 than the plants of New Zealand proper, we find that the wides 

 form 30 per cent, of the flora. In the plants that reach Stewart, 



