XVII C^SALPINIA 



193 



II that the seeds of inland plants sink and those of coast plants 

 float. 



My data, therefore, show that with the seeds of Caesalpinia 

 buoyancy goes with station and not necessarily with species. It is 

 probable, therefore, that with the two widespread species, C. bondu- 

 cella and C. bonduc, varying results will be obtained with seeds 

 from different localities, whether insular or continental, according 

 to the original station. The typically buoyant seeds of the former 

 species may, as we have seen in Hawaii, lose their floating powers 

 when they grow inland ; and the seeds of an inland species from 

 the mountains of Fiji sink at once. It is essential in interpreting 

 the results of experiments on the seeds of these plants to be 

 acquainted with the stations ; and in this respect those of the 

 Tahitian plants may be regarded as probable test cases. We have 

 seen that in Tahiti, C. bonduc is an inland plant, and C. bonducella 

 usually a beach plant ; and I have no doubt that experiments in 

 that island on the seeds of these two species from the particular 

 stations just referred to will give results in agreement with the 

 principle here laid down. 



With reference to the duration of the floating powers of these 

 seeds it may be observed that a seed of Caesalpinia bonducella, 

 originally found stranded on the beaches of Keeling Atoll, floated 

 after a year in sea-water as buoyantly as at the commencement of 

 the experiment. Seeds of Fijian littoral plants of both 

 C. bonducella and C. bonduc floated in my experiments after 

 two and a half years' immersion in sea-water, showing no change 

 whatever. Some of the seeds removed at the end of the first year 

 were filed and placed in soil, when they germinated healthily. In 

 Chapter IX it is pointed out that some buoyant seeds of other 

 Leguminous plants, such as Mucuna urens, would be apt to 

 germinate abortively and to sink in crossing the more heated areas 

 of tropical seas. The seeds of Caesalpinia, judging from my experi- 

 ments and observations noted on page 84, seem to be quite proof 

 against such risks. This was well brought out in an experiment 

 where seeds of the two species of Caesalpinia were kept afloat for two 

 and a half years in a vessel of sea-water together with seeds of 

 Mucuna and Strongylodon. None of the Caesalpinia seeds at- 

 tempted to germinate in the sea-water ; but with the other genera 

 some of the seeds began to germinate, and sank in the course of 

 the first warm season, when the water-temperature ranged from 

 75 to 90° Fahr. 



The seeds develop their buoyancy during the great contraction 

 VOL. II O 



