xvii C^SALPINIA ' 183 



(5) Although the seeds offer a striking example of dispersal by- 

 currents, since they are to be found stranded on beaches over much 

 of the globe, from within the Arctic Circle to the Coral Sea, in few 

 plants could the character of the buoyancy and the structure 

 connected with it have so little claim to be considered as adaptive 

 in their nature. At least 50 per cent, of the seeds sink in sea-water, 

 and the cause of the buoyancy of the other seeds is only to be 

 connected with the large size of a cavity producea by the shrinking 

 of the embryo within the seed tests during maturation. 



C^SALPINIA 



This genus is represented in the tropics of both the Old and 

 the New World by some eighty species of trees, shrubs, and 

 climbers, some of which are noted for their dye-woods, and others 

 for the beauty of their flowers. In the Pacific islands the botanist 

 is only concerned with three widely distributed species, all more or 

 less littoral in their station, and in great part dispersed by the 

 currents, namely, Caesalpinia nuga (Ait), C. bonducella (Flem.), and 

 C. bonduc (Roxb.). 



With Csesalpinia nuga we have little to do, since, although 

 widely distributed in tropical Asia and the Malayan region, and 

 reaching to both New Guinea and North Australia, it has not 

 apparently penetrated into the Pacific further east than the Solomon 

 and New Hebrides groups. I found it growing on the coasts of 

 the larger islands of the Solomon group, but no observations were 

 made on its mode of dispersal. However, as its seeds were 

 identified at Kew (^Bot. Ckall. Exped. iv, 311) amongst my 

 collections of stranded drift from those islands, it would appear to 

 be to some degree dispersed by the currents, though since it does 

 not extend far into the Pacific, its capacity for dispersal by this 

 agency would seem to be limited. Schimper includes it among 

 the strand-plants of the Indo-Malayan region. 



It is with the other two species, Cassalpinia bonducella and 

 C. bonduc that we are especially interested. Their extremely hard, 

 marble-like seeds at once attract attention, and when pale in colour 

 they look not unlike quartz pebbles as they lie stranded on a beach. 

 The prickly pods and the recurved prickles of the leaf-branches 

 often make these plants provokingly evident to a stranger. 

 Though usually to be characterised when growing on a beach as 

 straggling shrubs, they will often climb trees when opportunities 



