MISCELLANEOUS PLANTS 



253 



Whilst it is a plant of the beach and of the dunes on the coasts of 

 Cuba (Harshberger, p. 673), it seems to be most characteristic of 

 inland districts in Jamaica, occurring, as we learn from the work 

 of Fawcett and Rendle, at heights of from 2000 to 3000 feet. See- 

 mann, however, observes that it is common on the sea-beach on the 

 Pacific side of the Panama Isthmus (Bot. Voy. H.M.S. Herald). 

 Whilst its range is said to cover the region between South Florida 

 and Buenos Ayres. its distribution seems to be fitful in the West 

 Indies, and I find no reference to it in my notebooks. 



It would seem that in the New as in the Old World the fruit- 

 eating pigeons have taken a more active part in its dispersal than 

 the currents. Reference may here be made to the fact that this 

 is one of the plants that established themselves on Verlaten Island 

 after the complete destruction of its vegetation by the great eruption 

 of the neighbouring island of Krakatau in 1883. It was found there 

 by Ernst and his party in 1906 (Ernst's New Flora of Krakatau, 



P- 37 )' ... 



The distribution of the species of Ximenia, only five being known, 

 is suggestive of a genus that owes its representation in both the 

 New and the Old World to its original dispersion from a common 

 centre in high northern latitudes in an age when warm climatic 

 conditions prevailed in those regions. It seems difficult to look for 

 any other satisfactory explanation in the case of a genus which has 

 one species that is found round the tropical zone, a second confined 

 to Mexico, a third to Brazil, a fourth to South Africa, and a fifth 

 to New Caledonia. Yet alternative explanations are possible, 

 though not necessarily hostile to Dyer's hypothesis, even though we 

 cannot regard them with approval. Thus, one may regard all the 

 localised species as derivatives of the plant that ranges round the 

 tropical zone. From this point of view it might be supposed that 

 Ximenia americana, in dropping species, so to speak, in different 

 parts of its range, has played on a large scale the role of a highly 

 variable polymorphous species in the Pacific archipelagos. Here 

 a solitary species, the sole representative of its genus and ranging 

 over the tropical Pacific, becomes ultimately in each group of islands 

 the parent of a number of peculiar species, the same process being 

 also exemplified in the individual groups (Plant Dispersal, p. 333, 

 etc.). Nevertheless, such an explanation would not account for the 

 original occurrence of the parent species in the ocean-severed regions 

 of the tropics. Either we must regard it as having travelled from 

 its birthplace in the tropics around the globe through the agency 

 of birds and currents, or we must view it as having been originally 

 spread over the diverging land-masses of the globe from a common 

 centre in the north. 



