THE EVOLUTION OF HERBACEOUS PLANTS 301 



plained (by Darwin') as due to the fact that the lessened competi- 

 tion between the members of an insular flora allowed many plants to 

 grow there into shrubs and trees which on the mainland could never 

 succeed in attaining more than a herbaceous stature. From what 

 we have seen as to the evolution of herbs this explanation appears 

 inadequate, and it implies that, in many cases, herbs must have lost 

 their great advantage of being able to pass from seed to seed in a 

 single season. Insular floras appear rather to be relics of the ancient 

 Tertiary vegetation which once flourished on the adjacent mainlands 

 but which has been more or less superseded there by an influx of 

 new plants, most of them herbs. The many striking differences in 

 flora between Juan Fernandez and adjacent Chile; the Canaries 

 and adjacent Morocco; St. Helena and adjacent South Africa; and 

 Socotra and adjacent Somaliland seem to point to this conclusion. 

 Strongly in favor of such a view are also the very numerous floral 

 resemblances exhibited between distant islands or between islands 

 and distant continents. The occurrences of shrubby species of 

 Plantago only in Hawaii, Juan Fernandez, and St. Helena; of 

 phyllodineous Acacias only in the Mascarene region, Hawaii, and 

 Australia; of related shrubby Compositae in Hawaii, Tahiti, the 

 Galapagos, and Juan Fernandez, and of numerous related species 

 in the Canaries, South Africa, and Socotra constitute a few of 

 many instances of such distribution. The very large proportion 

 of woody plants compared to herbaceous plants in these insular 

 floras and the high degree of endemism of the former as opposed 

 to the latter strongly favor the theory that these particular islands 

 do indeed support a very ancient type of organic life, and that 

 since the opening of the Tertiary at least they have not been 

 intimately connected with any large continental area. 



Other isolated islands or archipelagoes, such as Bermuda and the 

 Azores, possess as high a percentage of herbaceous plants in their 

 vegetation as do the adjacent continental areas, and they likewise 

 have a very small endemic element. We are forced to conclude, 

 on evidence both from the flora and from the composition of the 

 vegetation, that such islands have appeared, or at least have 

 received their plant life, in comparatively recent times. 



' C. Darwin, Origin of Species, 6th ed., p. 413. 



