4 A NATURALIST IN THE PACIFIC chap. 



more than a problem of means of dispersal, or a problem of 

 station, or a problem of plant migration connected with climatic 

 changes. It is something a great deal more than all three, 

 since it is indissolubly connected with a past, of which unfortun- 

 ately we know very little. Let us take it to be a question of 

 means of dispersal, and then in imagination transporting ourselves 

 to the Scandinavian coast, let us gather up the stranded West 

 Indian beans of Caesalpinia, Mucuna, and Entada, that have been 

 drifted there for ages by the Gulf Stream, and lie in some cases 

 semifossilised in the adjacent peat-bog. Was ever dispersal so 

 utterly purposeless as this ? Yet here lies a principle of plant- 

 dispersal that is fundamental. We see it in the thistle-seed floating 

 seaward in the wind. Nature never intended its pappus for such 

 an end. It was formed for quite another purpose, yet it aids 

 largely the dispersion of the plant. What can be more significant 

 than that ? 



Or let us take it to be a matter of station. Given time and the 

 recurrence of the same conditions, with others I once imagined that 

 we could explain most things in plant-distribution, whether of 

 plants at the coast or of plants inland, whether of plants of the 

 alpine peaks or of plants of the plains, or of plants of the river or 

 of the pond. Time, it was held, had long since discounted the 

 means of dispersal, and distribution became merely an affair of 

 station. But the supplanting of many indigenous species of a flora 

 by introduced species is a common story in the plant-world ; and 

 such a view needs no further discussion here. Nor is distribution 

 only concerned with plant-migration. Any theory of the origin of 

 alpine floras on tropical mountains will have to explain the pre- 

 sence of the temperate genera, Geranium and Sanicula.not alone on 

 the summits of the mountains of Equatorial Africa and Madagascar, 

 but on the uplands of Hawaii in mid-Pacific, where also are found 

 Ranunculus, Vaccinium, Fragaria chilensis (the Chilian strawberry), 

 and Drosera longifolia. 



Taking genera of different stations each in their turn, and fol- 

 lowing up the clues thus afforded, it would be possible to find 

 support for all the reputable views relating to plant-distribution. 

 The wide range of aquatic plants under conditions that completely 

 change the character of the terrestrial vegetation, such, for in- 

 stance, as Myriophyllum and Ceratophyllum, might be plausibly 

 attributed to the relative uniformity of the conditions of aquatic 

 life both in time as well as space. The occurrence of Vaccinium 

 on mountain-tops over most of the world, even on the highlands 



