226 PLANTS, SEEDS, AND CURRENTS 



category as M. citrifolia, the pyrenes of which are often dispersed by 

 currents. 



It is shown in my previous work that the fleshy fruits of this 

 genus must often attract birds, and that the pyrenes could be readily 

 transported by frugivorous birds across tracts of ocean. Nearly all 

 of the fifty known species are inland plants ; and the indications are 

 that only the littoral plants possess buoyant pyrenes, the bladder- 

 like cavity being either absent or but slightly developed in the 

 pyrenes of inland species. From its range over the warm regions of 

 the globe Morinda is a very interesting genus for the student of 

 distribution. Very noteworthy is it that quite 60 per cent, of the 

 species are confined to islands, large and small, in Malaya and in the 

 Indian and Pacific Oceans. 



Though this is predominantly an Old World genus, not more than 

 15 per cent, of the species being restricted to America, the peculiar 

 New World species have originated in several localities, as in Mexico, 

 Guatemala, Yuca tan, Panama, Venezuela, Haiti, and Cuba. Nearly 

 all these localities are given in the Index Kewensis. Urban has 

 described a new species from Haiti under the name of M. buchii 

 (Symb. AntilL, I., 481) ; and Dr. Greenman has in recent years dis- 

 tinguished a new species, M. yucatanensis, which had been previously 

 referred to M. royoc. It is found in brushlands and forests in the 

 interior of Yucatan (Publication 126, Botanical Series of the Field 

 Columbian Museum, Chicago, 1907). Nothing, however, is said of 

 the distinctive structure of the pyrenes. The plant is known in 

 Yucatan under the Mayan name of " Joyoc " (Hoyoc). If, as seems 

 probable, this is a plant of the Royoc series, then we might here be 

 presented with the case of a derivation of an inland species from a 

 littoral species, a subject generally discussed in my book on Plant 

 Dispersal. 



As regards the history of the American representatives of Morinda, 

 I venture to hold, in spite of the numerical superiority of the genus 

 in the Old World, that, like many other genera common to the 

 western and eastern hemispheres, it originally spread from a common 

 centre in high northern latitudes during one of the warm geological 

 periods in those regions. 



Omphalea triandra, L. 



This tree, the " cobnut " of Jamaica, is interesting from the stand- 

 point of dispersal by currents, since its seeds float buoyantly and 

 occur occasionally in the drift on Jamaican beaches. The tree 

 grows in hills behind St. Anne's in that island, and it was in this 

 neighbourhood that I found the seeds on the beaches. The seeds 

 are globose, about an inch in size, brown-coloured, and not unlike 

 chestnuts in look. The buoyancy arises from a large internal cavity 

 and also from the independent floating power of the kernel, portions 

 of the albumen floating in water. The brown covering is seemingly 

 waterproof, and no doubt the seeds would float for some time. It 

 is, however, very doubtful whether they could find their way to a 

 suitable inland station when stranded on a coast. Since the seeds 



