35^ 



SKOTTSBERG 



improbable. Araceac are pleiitihil in luiinid tropical climates, and some islands, 

 the Hawaiian for instance, ouL^ht to offer a suitable environment; still there is not 

 a sin<^le native species. And it is strange that orchids, with their dust-like seeds, 

 should be, if not altogether absent, so few, becoming fewer and fewer as we proceed 

 east from Mala\'sia and Melanesia; cf. ?/cV, map 21. However, the seeds, even 

 if carried far, rarely are able to retain their viability long enough to become 

 established, should they haj)pen to strike a spot where they can germinate. I be- 

 lieve that also where we find a very rich orchid flora most of the species occupy 

 restrictetl areas; their advance over land is slow. A species introduced on pur- 

 pose will, in rare instances, become naturalized, but I cannot remember ever 

 luning heard of an adventitious orchid. Taking all these circumstances into account, 

 the poverty of distant islands, even if temporarily connected with other lands, 

 is perhaps not altogether incomj)rehensible. Besides, the submerged links may, 

 for all we know, have been {)oor in legumes, arum lilies and orchids. CAMPBELL, 

 admitting that the total absence oi Araucana, Agat/us, Podocarpus, Ficus and Ara- 

 icac in oceanic islands of the Pacific is a valid objection, not easy to explain, 

 suggests that perchance they once did exist there but were destroyed by volcanic 

 eruptions [^6. 181). 



'J he prcpcnidcraiicc of woody plants in oceanic islands. — Hemsley (727. 31) 

 em|)hasized the prominent part taken by arboreous and shrubby species in many 

 islands and pointed out that in some cases they belong to otherwise herbaceous 

 families. Many peculiar genera of Compositae are confined to islands such as 

 Hawaii, (ialapagos, and Juan Fernandez, and are scattered over Polynesia (see 

 ,VcS'. map 20), and in the Atlantic (Macaronesia, St. Helena) and Indian oceans 

 (.Socotra, the Seychelles, Mascarene Islands); arboreous Compositae are, as HemS- 

 l.KV just])' remarks, by no means restricted to island habitats but numerous in 

 tropi( al regions of the continents, particularly in America. Both Hawaii and Juan 

 I'Y-rnandez offer good examples of woody plants belonging to otherwise herba- 

 ceous families or genera, but Hkmsi.kv's statement p. 31 about Gwinera\\\]\x2S\. 

 I'V-rnandez "caulescent species unknown elsewhere" — is erroneous, for they are 

 just as caulescent in Hawaii; besides, they are not woody, but herbaceous. 



Scarcity of herbaceous species, especially of tJierophytes. — Native annuals and 

 biennials are rare in islands. They cannot have been less capable of migrating 

 across the sea than trees or shrubs, nor could soil or climate prevent them from 

 getting established; this is at once disproved by the countless herbaceous weeds 

 brought by man which threaten to overrun so many islands. The reason must 

 be historical. If it is true that life forms with a woody stem are the most ancient, 

 and if tlie original stock making u|) island floras dates back to before the rise of 

 herbs, a period during which the distribution of land and sea was another than 

 now, we can exj)lain the high {)r()p()rtion of arborescent species in islands iso- 

 lated since millions of \'ears. 



1-j'ideiice for a greater antiquity of lignifed angiosper)ns. — The angiosperms 

 originated in the Mesozoic and are traced back to the Lower Cretaceous. The 

 tree form was the res|)onse to a warm and humid climate. These problems were 

 subjected to a comprehensive analysis by SiNNOTT and I. W. Bailey [22f), whom 



