108 THE FURTHER EXTENSION OF THE [pt. u 



mined for each group of the Compositae, and it is shown that on 

 the Avhole it increases with the increasing age of the group as 

 deduced from phyletic, morphological, and geological con- 

 siderations. This agreement forms a strong argument both for 

 the general correctness of Age and Area, and for that of the 

 previously deduced genetic relationships of the different groups 

 of Compositae. 



In the second part of the chapter Prof. Small takes up the 

 application of Size and SjDace, showing that it holds very well 

 indeed as a general rule in this family, so that here, as in other 

 cases, "both the average generic area and the average number 

 of species per genus are closely related to absolute age." Age, 

 Size, and Space go together. 



Mrs Reid then takes up the application of Age and Area to 

 the fossil botany of comparatively recent times, especially the 

 Pliocene and Pleistocene. She shows how great have been the 

 migrations to and fro, north and south, of the floras of the 

 north temperate zone, and discusses the applicabilit}^ of this 

 proved migration to the flora of New Zealand, leaving the 

 question finally open for settlement by geological evidence. Dis- 

 cussing then the flora that at one time occupied the complete 

 circle of the north temperate zone, and which is now confined 

 to North America or to China, or to both, and often a good deal 

 broken in distribution, she shows that the existing dispersal 

 may probably be attributed mainly to the effects of the Glacial 

 period. 



It is then pointed out that it is this unquestionable fact that 

 a good many existing strictly localised or endemic species are 

 survivors of races that once flourished widely, that offers the 

 greatest stumbling block to the acceptance of Age and Area, but 

 that there is no insuperable difficulty in the acceptance both of 

 this fact and of Age and Area, for the latter is reasoning from the 

 mass, the former from the individual, and while perhaps 1 per 

 cent, of the grand total of endemic species are relics, the rest are 

 not, and in reasoning about the mass the former are quite lost. 

 There is good evidence to the effect that many or most of these 

 survivals are due to the effect oi' the Glacial period, and on the 

 whole, therefore, the verdict is in favour of Age and Area. 



Endemism and Distribution of Species are then considered in 

 Chapter xv, and it is shown that the phenomena presented by 

 endemic species in their distribution are simply a miniature of 

 those presented by species in general, and that the distribution 



