Ill THE LESSON OF THE BRITISH FLORA 25 



temporarily entangled in the glumes, the proportion of seeds and 

 fruits that sink at once or in a few days would probably have been 

 about 80 per cent. Then again, since the plants from stations 

 where buoyant seeds and seedvessels are most frequently found — 

 that is at the river-side, the pond-margin, and the sea-coast — are 

 much more completely represented in these experiments than those 

 from other stations, it would seem that even 80 per cent, is too low 

 a figure. Even if the 80 plants with the buo/ant seeds or seed- 

 vessels included all the species thus characterised, which they 

 certainly do not, we should obtain an estimate for the British 

 flora (rather over i,2CXD species of flowering plants) of about 93 per 

 cent, with non-buoyant seeds or fruits. This is, of course, too high. 

 It is, however, very probable that the proportion of plants with 

 non-buoyant seeds or seedvessels for the whole British flora is 

 about 90 per cent. 



This proportion of plants with non-buoyant seeds or seed- 

 vessels, that is to say, of those that sink at once or within a week, 

 is also approximately correct for the flora of one of the larger 

 islands of the tropical Pacific. The data at my disposal only 

 enable me in the cases of Fiji and Hawaii to fix it at between 

 95 and 85 per cent, or on an average 90 per cent. With the floras 

 of continental regions the proportion would doubtless be markedly 

 higher. That seeds and seedvessels as a rule possess but little 

 buoyancy was a sound conclusion of Darwin, and one, as he 

 remarked, that is in accordance with the common experience 

 of gardeners. Thuret, after experimenting on the buoyancy in 

 sea-water of the seed or seedvessels of 251 species of plants, 

 belonging to JJ families and to various regions, found that 

 scarcely two per cent, had any powers of flotation, all the 

 rest sinking at once or in a few days, a result that led De 

 Candolle in a note to this memoir to reiterate his opinion 

 regarding the inefficacy of currents as plant distributors. Thuret, 

 however, did not select many of his plants from stations where 

 buoyancy is most frequently exhibited, and his estimate errs, 

 therefore, in imputing too little buoyancy to seeds in general. The 

 power of seeds and fruits to germinate after prolonged flotation in 

 sea-water has long been well established, and it is often illustrated 

 in this work, so that there is no need to dwell upon it here. (See 

 Note II.) 



Of the 240 species of British plants where sinking took place 

 at once or within a week, in about 50 per cent, the plants had dry 

 indehiscent fruits, such as we find in the genus Ranunculus and in 



