MISCELLANEOUS PLANTS 



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their germinative capacity. Yet, strange to say, the fruits of these 

 sister species, so similar in station and in habit, exhibit very different 

 types of buoyancy. In both cases the maintenance of the floating 

 powers depends on the " stone " ; but there the similarity ends. In 

 both plants the fresh drupe floats in sea-water, and the buoyant 

 stone is freed in a few days by the decay of the fruit. This, however, 

 is not the usual course of events in nature, since the fallen drupe 

 generally loses its soft parts whilst lying on the sand beneath the 

 bush, and it is the more or less dry stone that is swept into the sea. 

 The stones form a regular constituent of the smaller beach-drift in 

 the different parts of the tropics where the two plants grow. 



I will first take the West Indian species, Sc. Plumieri. Should 

 the fresh black drupes get into the sea, experiment shows that they 

 will sink in two days, the buoyant stone, on being freed from the 

 decaying fruit, soon floating to the top. But, as just remarked, it 

 is the more or less bared stone that is usually picked up by the wave 

 from the beach. These stones, ovoid in form, prominently tubercled 

 on the surface, and 9 or 10 mm. in length, do not possess buoyant 

 tissue of any sort, neither the hard material of the stone nor the seed 

 within possessing any floating power. The outer cork-like covering, 

 which, as described below, endows the stones of Sc. Kcenigii with 

 buoyancy, is not here represented. The floating capacity of the 

 stone of Sc. Plumieri is due to the circumstance that only one of its 

 two cells holds a seed. The empty cell, which is water-tight and 

 usually contains the seed envelopes, gives floating power to the 

 stone. This can be proved in different ways. The most striking 

 proof is this. If we take a buoyant stone and remove the portion 

 containing the empty seed-cavity, it sinks at once. But if we 

 remove the portion holding the seed, it floats still more buoyantly, 

 almost like a piece of cork. It does not follow that the two-celled 

 stones of this plant never have both cells filled with a seed. My 

 observations, however, indicate that stones with one cell empty 

 predominate. In fact, two- seeded stones very rarely came under 

 my notice. 



Though it is usually the bared stone of Sccevola Kcenigii that is 

 picked up by the waves as it lies on the beach, the fresh drupe may 

 at times be carried off by the sea. In that case it floats buoyantly, 

 and when after a few days' immersion it loses its white, fleshy cover- 

 ing, the stone remains at the surface. As studied in the homes of 

 the plant by Schimper (p. 172) and myself, the cause of the buoyancy 

 lies in a layer of cork-like, air-bearing tissue investing the stone 

 proper. If this covering is removed the stone sinks, neither the 

 hard material composing it nor the seeds possessing any floating 

 power ; and I may add that the two cells of the stone in each case 

 hold a seed, so that the question of buoyancy of the type presented 

 in the instance of Sc. Plumieri is not raised. It may be remarked 

 that the stone proper of Sc. Kcenigii is much smaller than that of 

 the West Indian species, being rounded, about 5 mm. across, and 

 slightly tubercled. 



The stones of the drupes of these two species of Sccevola represent 

 two quite different types of buoyant fruits, types that are describe d 



