214 PLANTS, SEEDS, AND CURRENTS 



beach fully exposed to the sun and weather. The tough, fleshy 

 seed of the living fruit here dries up and hardens until it has the 

 consistence and appearance of a stone, a change affecting both the 

 seed that has germinated and the seed that has not. In this new 

 state, however, the seed retains the normal amount of hygroscopic 

 water, such as we would look for in dead vegetable substances of the 

 same nature. As is pointed out in my book on Seeds and Fruits 

 (p. 232), it loses about 12 per cent, of water when exposed to a tem- 

 perature of 100° C, and there is no indication of its having assumed 

 the characters of inorganic substances. 



On some beaches most of the stranded fruits contained these hard, 

 stone-like seeds. Thus, on a beach in the Black River district about 

 25 per cent, possessed either no seeds or seeds far advanced in decay, 

 the rest having dead seeds that had experienced the stony induration 

 above described. Placed in a collection of fossil fruits from some 

 clay formation, one of these oblong, indurated seeds of Grias cauliflora 

 might pass as a fossil fruit, particularly when a longitudinal section 

 had been made so as to expose the central axis in relief. At all events, 

 they might be readily fossilised in ordinary fresh-water deposits, 

 and it is quite likely that some puzzling organic forms in the old plant- 

 beds may be petrified seeds which, as in the Barringtonice and 

 Lecythidece, are merely greatly enlarged hypocotyls. 



Hibiscus elatus, Sw. (Paritium elatum, G. Don) and Hibiscus 

 tiliaceus, L. (Paritium tiliaceum, A. Juss.) 



At some future time I may publish my notes on the different 

 species of the Hibiscece from the distribution standpoint, a subject 

 already partially dealt with in my work on Plant Dispersal. Here 

 I will endeavour to bring my methods to bear on the elucidation 

 of the causes of the great difference in range between these two 

 allied species, one (H. elatus) confined to a relatively small area in 

 the New World, the other (H. tiliaceus) occurring all around the 

 tropical zone. Hibiscus tiliaceus is a species with which I have 

 long been familiar in many parts of its range — on the Atlantic and 

 Pacific sides of America, in various Pacific islands, in the Malayan 

 region, and in the Keeling Islands in the Indian Ocean. 



On making the acquaintance of Hibiscus elatus in Jamaica I recog- 

 nised that it gave me an opportunity of comparing two allied species 

 (both of them placed under Paritium) of widely different ranges, and 

 I asked myself whether this great contrast in range could be asso- 

 ciated with differences in behaviour, as regards station, means of 

 dispersal, etc., or whether, assuming the intervention of man, it was 

 connected with the utility of one tree and the uselessness of the 

 other. Obviously here was an opportunity of making a flank attack 

 on the problems concerned with H. tiliaceus. It soon appeared, 

 however, that the determining factor was concerned neither with 

 man nor with means of dispersal, but with differences of station, and 

 that the same point was raised, to which my attention had been 

 drawn in various genera in the Pacific islands, namely, that in a genus 

 possessing littoral and inland species, the first had often very wide 



