INTRODUCTORY ESSAY. xxv 



We thus observe that the want of an Arctic or Antarctic Flora at all in the Pacific islands, 

 and the presence of an Arctic one in the American Alps, are the prominent features ; and I shall 

 confine my remarks upon these to the fact that, with regard to the isolated islands of the Pacific, 

 they are situated in too warm a latitude to have had their temperature cooled by changes in the rela- 

 tive position of land and ocean, so as to have harboured an Antarctic vegetation. "With regard to the 

 South American Alps, there is direct land communication along the Andes from Arctic to Antarctic 

 regions ; by which not only may the strictly Arctic genera and species have migrated to Cape Horn, 

 but by which many Antarctic ones may have advanced northward to the equator*. 



There is still another point in connection with the subject of the relative antiquity of plants, and 

 in adducing it I must again refer to the ' Principles of Geology/ where it is said, " As a general rule, 

 species common to many distant provinces, or those now found to inhabit many distant parts of the 

 globe, are to be regarded as the most ancient .... their wide diffusion shows that they have 

 had a long time to spread themselves, and have been able to survive many important changes in 

 Physical Geography f." If this be true, it follows that, consistently with the theoiy 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, CaUitriche 

 verna, Cardamine hirsuta, Epilobium tetragonum, and many others. 



On the other hand, it must be recollected that there are other causes besides antiquity and 

 facility for migration, that determine the distribution of plants ; these are their power, mentioned 

 above, of invading and effecting a settlement in a country preoccupied with its own species, and their 

 adaptability to various climates : with regard to the first of these points, it is of more importance 

 than is generally assumed, and I have alluded to its effects under Sonchus, in the body of this work. 

 As regards climates, the plants mentioned above seem wonderfully indifferent to its effects!. 



Again, even though we may safely pronounce most species of ubiquitous plants to have outlived 

 many geological changes, we may not reverse the position, and assume local species to be amongst the 

 most recently created; for whether (as has been conjectured) species, like individuals, die out in the 

 course of time, 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 

 others), they must in either case become scarce and local while they are in process of disappearance. 



In the above speculative review of some of the causes which appeal' to affect the life and range 

 of species in the vegetable kingdom, I have not touched upon one point, namely, that which concerns 

 the original introduction of existing species of plants upon the earth. I have assumed that they have 

 existed for ages in the forms they now retain, that assumption agreeing, in my opinion, with the facts 

 elicited by a survey of all the phenomena they present, and, according to the most eminent zoolo- 



* Why these Antarctic forms have not extended into North America, as the Arctic ones have into South America, 

 is a curious problem, and the only hypothesis that suggests itself is derived from the fact that though the Panama 

 Andes are not now sufficiently lofty for the transit of either, there is nothing to contradict the supposition that they 

 may have had sufficient altitude at a former period, and that one which preceded the advance of the Antarctic species 

 to so high a northern latitude. 



f Principles of Geology, ed. 9. p. 703. 



X Mr. Watson (Cybele Brilannica) gives the range of CaUitriche in Britain alone as including mean tempe- 

 ratures of 40° to 52°, and as ascending from the level of the sea to nearly 2000 feet in the East Highlands of 

 Scotland. Montia, according to the same authority, enjoys a range of 36° to 52°, and ascends to 3300 feet 

 bium, a temperature of 40° to 51°, and ascends to 2000 feet; Cardamine, a temperature of 37° to 52°, and ascends 

 to 3000 feet. 



