314 A NATURALIST IN THE PACIFIC chap. 



PSYCHOTRIA (Rubiacese). 



We find in this large genus of the Old and New Worlds a 

 typical example of the plants with fleshy drupes containing hard 

 pyrenes that represent, from the standpoint of dispersal, a common 

 Rubiaceous type of plant in the tropical Pacific. Such plants, 

 of which those of Coprosma and Nertera may be cited as other 

 instances, are in a generic sense always widely distributed in these 

 islands. They are eminently suited for dispersal by frugivorous 

 birds ; and it is a matter for surprise, therefore, that in a genus 

 like Nertera the solitary Pacific species has such a wide range, 

 whilst with Psychotria and Coprosma the numerous species are 

 usually restricted to particular groups. Genera doubtless have 

 their periods of development and decadence in the Pacific, and 

 probably Nertera is to be regarded as a decadent genus. These 

 Rubiaceous genera, however, appear to be well fitted for the 

 investigation of the centres of dispersal of particular genera and of 

 their relative age. 



The Psychotrias in these islands are typically shrubs of the 

 shady woods, and they may be seen thriving best where the forest- 

 growth is rank and the humidity greatest. Their bright red ovoid 

 drupes, which range from eight to twenty-five millimetres in length 

 (J to I inch), would readily attract birds, and their crustaceous 

 pyrenes, that vary between five and eight millimetres (-|- to J inch) 

 in length, would pass unharmed through a bird's digestive canal. 

 That fruit pigeons can distribute their seeds over the Pacific has 

 been long established, and Mr. Hemsley includes Psychotria 

 amongst those genera which, from the collections of fruits and seeds 

 found in the crops of fruit-pigeons, made by Professor Moseley, 

 myself, and others, in the groups of the Western Pacific, are " known 

 to be dispersed by birds in Polynesia " {Introd. Bot. Chall. Exped., 

 p. 4S). It is thus hardly necessary to point out that neither the 

 entire fruits nor the separate pyrenes could be transported by the 

 currents, my observations showing that in both cases they sink at 

 once or in a day or two. 



Psychotria, however, is an enormous genus including, according 

 to the Index Kewensis, some 600 or 700 described species, dis- 

 tributed in the tropics all over the world, and also extending into 

 subtropical regions, the greatest concentration being in America. 

 It is described in the Genera Plantarum as a polymorphous genus 

 distinguished by no certain characters from some other genera of 



