xxvi PISONIA 



347 



islands of the Indian and Pacific Oceans, extending to North-East 

 Australia and to New Zealand. On account of the unusual 

 capacity for dispersal possessed by this species — a subject to be 

 immediately discussed — the tendency to specific differentiation has 

 been kept in check, though the process has gone farther in some 

 groups than in others, as in the case of Hawaii, where Hillebrand's 

 endemic species has, however, been included by Drake del Castillo 

 in his polymorphous species, P. umbellifera. 



The fruits of this genus possess no capacity for dispersal by 

 currents. They never came under my notice either in floating 

 or stranded seed-drift, and have little or no buoyancy. Prof. 

 Schimper, experimenting on the well-dried fruits of Pisonia 

 aculeata, a seaside shrub common in America and in the Old 

 World, and destined probably to be brought by the systematist 

 into touch with the polymorphous P. umbellifera, found that they 

 sank in a day or two (Ind. Mai. Strand-flora, p. 156). Dismissing 

 the agency of the current, he looked to that of the bird for the 

 explanation of the dispersal. The probability of the effectiveness 

 of this last-named agency has long been surmised. It attracted 

 the notice of Darwin and especially invited the attention of another 

 student of plant-dispersal, Dr. H. O. Forbes. The long, narrow, 

 often fusiform fruits are invested by a somewhat coriaceous 

 perigone and range from less than an inch to three inches in 

 length (2 — 7 - 5 cm.). They excrete a very viscid fluid often in 

 quantity, and sometimes also possess glandular spines. The 

 Hawaiians, according to Hillebrand, used this material as bird- 

 lime for catching birds, and the fruits, he says, will stick fast to the 

 paper in the herbarium for years. In that group I often found the 

 fruit adhering firmly to my clothes. Writing of these trees on 

 Keeling Atoll, Forbes observes that their sticky fruits are often 

 such a pest to birds roosting in their branches that they have 

 proved fatal to herons and boobies by collecting in their plumage. 

 " It is easy to perceive," he remarks, " how widely this tree might be 

 disseminated by the birds that roost on it" {The Eastern Archi- 

 pelago, p. 30). In New Zealand, as we learn from Kirk, the viscid 

 fruits of Pisonia brunoniana attract small birds which become 

 firmly caught and die miserably. A cat has been known to wait 

 under a tree watching its opportunity of preying on the entangled 

 birds. Sir W. Buller states that the New Zealand fruit-pigeon 

 feeds at times on the green fruits of P. umbellifera ; and we can 

 infer that it occasionally carries off some of the riper fruits in its 

 feathers. 



