4 INTRODUCTORY [pt. i 



circumstances in the animate or the inanimate world have 

 occurred to restrict the range which they may once have 

 obtained. 



Hooker (55a, p. xxv), in the same year, 1853, quotes the first 

 passage from Lyell, and goes on 



If this be true, it follows that consistently with the theory of 

 the antiquity of the alpine flora of New Zealand, we should find 

 amongst the plants common to New Zealand and the Antarctic 

 Islands some of the most cosmopolitan, and we do so in Montia 

 fontana, Callitriche verna, Cardamijie hirsida, Ejnlohium tetra- 

 gonum and many others.... On the other hand, it must be recol- 

 lected that there are other causes besides antiquity and facility 

 for migration, that determine the distribution of plants, -these 

 are their power... of invading and effecting a settlement in a 

 country preoccupied with its own species, and their power of 

 adaptability to various climates... though we may safely pro- 

 nounce most species of ubiquitous plants to have outlived many 

 geological changes, we may not reverse the position, and assume 

 focal species to be among the most recently created, for species, 

 like individuals, die out in the course of time; whether following 

 some inscrutable law whose operations we have not yet traced, 

 or whether (as in some instances we know to be the case) they 

 are destroyed by natural causes (geological or other) they must 

 in either case become scarce and local while they are in process 

 of disappearance. 



It is thus clear that the subject of Age and Area is by no 

 means new. Until comparatively recently I was not aware of 

 the above very striking quotations, and it is interesting to find 

 that my experience of actual distribution in many lands has led 

 me, as it has led Guppy and many more, to much the same 

 conclusions as those reached by two authorities so great as Lyell 

 and Hooker. Had it not been for the appearance and rapid rise 

 of the great theory of Darwin, with its ine\'itable diversion of 

 effort into other and at the time much more profitable lines, it 

 is evident that Hooker or some other worker of an earlier time 

 would have discovered not only the principle which I have 

 termed Age and Area, but also the many and remarkable con- 

 clusions to which it leads. 



During the last twenty years, since finishing my monograph 

 of the Indian Podostemaceae (116), I have devoted my spare 

 time to the study of geographical distribution. My studies of 

 that family had convinced me that the vital factors were not, 

 to any great extent, responsible for the existing dispersal of the 

 species, and in May, 1907, I published the first sketch of the 



