96 OBJECTIONS TO THE HYPOTHESIS [pt. i 



factorily explained^ does not in the least militate against the 

 hypothesis of Age and Area. Age and Area may seem to disagree 

 with other views as to this or that, but it is based upon very 

 clear and definite figures, which must either be controverted or 

 explained in some other way — they are far too striking to go 

 without any explanation. It is somewhat difficult to controvert 

 figures which simply represent bald facts, and if Age and Area 

 be not accepted, it is consequently necessary to have some other 

 hypothesis, which must be mechanical, owing to the fact that 

 the figures show such mechanical regularity. 



The objection is based largel}^ on the lui doubted fact that the 

 proportion of "swamped" genera is larger in the more outlying 

 of the big islands. But that mere isolation is not sufficient as an 

 explanation would seem to show in the fact that in the very 

 isolated islands round New Zealand the proportion is not so 

 high as in New Zealand itself. In New Zealand 127 genera out 

 of 329 show it, in the Kermadecs only 8 out of 62, in the Chathams 

 the same, and in the Aucklands 12 out of 64. In none of the 

 islands is the proportion anything like so high as in New Zealand, 

 and it is highest in the Aucklands, which Avere perhaps nearest 

 to an incoming stream of plants (131). On the other hand, the 

 number of genera which are swamped in New Zealand is 13 in 

 the Kermadecs, 38 in the Chathams (the most isolated), and 26 

 in the Aucklands, facts tending to show that the swamped 

 genera were in existence fairl}^ early opposite to the Chathams, 

 and therefore were rather old in comparison to some of the rest, 

 though e^'en in the Chathams the imswamped genera (29) are 

 almost as ninnerous. 



Another test that we may apply is to find the proportion of 

 *'swamped"genera in the northern and southern invasions of plants 

 into New Zealand (p. 79). The northern shows 45 out of 75 or 60 

 per cent., while the southern shows 36 out of 108 or 33 per cent. 

 We have seen that probability is in favour of the greater age in 

 New Zealand of the northern invasion, so that to some extent 

 this speaks in favour of the objection in a general and purely 

 local sense. But as only one herb {Elatostema) is "swamped" in 

 the noi'thern invasion, and all the shrubs but one {Veronica) in 

 the southern, it is, it seems to me, equally possible that swamping 

 may go with woody habit, and further tests are necessary. 



1 Small (103, pp. 189, 224) has suggested two explanations, both quite 

 probable; but as the phenomenon (as shown above) does not affect the 

 probability that Age and Area is a correct hypothesis upon which to work, 

 the question may be left out of consideration in this place. 



