xxvi GOSSYPIUM 353 



nesia), and is applied by the Fijians to Hibiscus esculentus and to 

 the introduced species of Gossypium. 



When in Hawaii I ascertained that neither the seeds of the 

 littoral plant, Gossypium tomentosum, nor those of two cultivated 

 species possessed any fitness for dispersal by the currents, the 

 scraped seeds sinking at once, whilst when covered with the wool 

 they floated only for a few days. Further references to G. tomen- 

 tosum in Hawaii are given in the index of this volume. 



TJie Last Stage of the General Dispersal of Plants of the 



Malayan Era. 



We arrive now at the close of the era of the general dispersal 

 of tropical plants, mainly Malayan, over the Pacific, and this 

 brings us down to our own age. The few genera that are still 

 dispersed have no peculiar species in particular groups. The 

 species which often range over all the groups, and retain as a rule 

 their characters in most of them, do not therefore display, except 

 in a few cases, that extreme variation which would give them a 

 place in the ranks of the polymorphous species. The dispersing 

 agencies, in fact, are sufficiently active to check marked variations, 

 and the process of isolation has scarcely begun. 



We perceive the reason of this when we look at the nine genera 

 which are taken as samples of this period, viz., Rhus, Osteomeles, 

 Viscum, Plectronia, Boerhaavia, Polygonum, Pipturus, Boehmeria, 

 and Dianella, most of them being known to be dispersed by birds 

 at the present day. Six of the genera possess fruits likely to 

 attract frugivorous birds ; whilst one of them, Boerhaavia, has 

 sticky fruits that would be apt to adhere to plumage. Actual 

 observations in the cases of Rhus, Viscum, and Plectronia establish 

 the fact of their dispersal by fruit-eating birds ; and there is no 

 difficulty in postulating the same agency for Osteomeles, Pip- 

 turus, and Dianella. A method by which Boerhaavia fruits 

 would be transported in the plumage of birds has been 

 observed by Mr. Lister ; whilst the nutlets of Polygonum are 

 known to afford food to a variety of birds and to be thus 

 distributed. 



In this period the plants all hail from the Asiatic side of the 

 Pacific. Three of the genera, Plectronia, Pipturus, and Dianella, 

 belong almost exclusively to the Old World. Five occur in both 

 the Old and New Worlds, but, as with Rhus, Viscum, Boerhaavia, 

 and Bcehmeria, are represented by Old World species in the Pacific, 

 VOL. II A A 



