366 



C. SKOTTSBERG 



If, on the other hand, the island group lies in the tropics and is large in area, the 

 islands of the group being close together, if the vertical relief be very great indeed . . . 

 if the precipitation be very variable ... if the soil be rich, but variable in porosity; if 

 the plant assemblages into which the waifs or colonists entered are not the end result 

 of severe plant competition; then the stage is set for the rapid differentiation of primary 

 types of agressive genera. 



The evidence available suggests that these genera never existed as such on the land 

 from where their immediate predecessors were derived, but that virile types, of the families 

 concerned, arrived as waifs from Malaysia, Australia, New Zealand, Central and North 

 America. Once they found themselves removed from their former severe competition 

 with other plants, they gave rise to the vigorous, endemic Hawaiian genera (p. 6i8). 



What Andrews depicts is an island which has reached maturity. It has risen 

 from the bottom of the ocean to an altitude where the moisture of the trade winds 

 is condensed, where there are leeward and windward slopes, dififerent habitats and 

 a rich soil. This island looks back on a very long history, but life begins to arrive 

 long before the island has come to rest. Aerial plankton will bring microscopic 

 green and bluegreen algae, bacteria, spores of all kinds and also air-borne seeds, 

 and some drift may be washed up on the shores. But to begin with there is little 

 humidity and hardly anything we can call soil, we need water before even the 

 most primitive organisms can exist, so that the island becomes fit to receive its 

 first settlers, microscopic algae, then mosses and lichens and mycelia of fungi, to 

 form soil where the first seeds can germinate and start to form an incipient vege- 

 tation cover and an abode for a soil fauna and flora. Lava cracks in cooling, some 

 water may stand in the fissures which form the starting point for further develop- 

 ment, a spectacle we have before our eyes where streams of lava are still formed. 

 Of higher plants, ferns are likely to be among the first to get established — GUPPY 

 even spoke of the "era of ferns"; a halophytic Asplenhmi is the only living thing 

 observed on the far-flung reef Sala y Gomez between Easter Island and South 

 America. 



An island in a comparatively recent stage, where there is plenty space for 

 new settlers, let it be that little comfort is as yet offered, would, we should think, 

 ofifer good opportunities for "virile and agressive" immigrants to get a foothold 

 and to become the ancestors of the most ancient element in the flora, but this is 

 not what ANDREWS says. In order to start an evolution of new species and genera 

 a very great vertical relief, a variable precipitation and a rich soil are the conditions, 

 but in order to get a rich soil cover we must have a closed vegetation cover, also 

 forest. Wallace {2y8. 295), speaking of St. Helena, very rightly said that "no 

 soil could be retained unless protected by the vegetation to which it in great part 

 owed its origin", and the same is true everywhere. If the change in environment, 

 the new living conditions, are the cause of \ariation, why did they not act until 

 the island was already more or less stocked with plants.- Were there no virile 

 species among the earliest immigrants which took possession of the land and formed 

 the oldest element of the flora .^ Was it lost among the later arrived aggressive 

 newcomers.- It is calculated that about 90% of the Hawaiian angiosperms are en- 

 demic, most of them belonging to endemic genera or to species very different from 

 their continental congeners. Do some of the most remarkable monotypical genera 



