THE BUOYANCY OF SEEDS AND SEEDVESSELS 



93 



littoral tree in Fiji, offer an interesting example. If we place 

 ioo seeds of a littoral tree in sea-water, we find that on the 

 average about 70 float If then we lower the density gradually, 

 some of the seeds begin to sink at once ; and on the removal of 

 the survivors to fresh water, about 47 will remain afloat. The 

 results may thus be stated : — Out of 100 littoral seeds, 30 are 

 specifically heavier than sea-water (1*025) ; 23 are between sea- 

 water and fresh water in specific weight ; whilst 47 are lighter 

 than fresh water (rooo). When, however, we take 100 seeds of 

 inland trees, we find that on the average 87 are heavier than sea- 

 water, 5 are in weight between sea-water and fresh water, and 8 

 are lighter than fresh water. The significance of these figures 

 becomes evident when we arrange them in curves. The combined 

 result for littoral and inland seeds is given in the diagram below ; 



and we see there, what is also indicated with the separate curves 

 that we are dealing with a double series, one concerned with 

 seeds lighter than fresh water, and the other with seeds heavier 

 than sea-water. The reader can himself supply the separate 

 curves for the littoral and inland seeds. The point, however, to 

 notice is that if a botanist with a statistical bent were to make a 

 miscellaneous collection of the seeds of the Vesi (Afzelia bijuga) in 

 one of the Fijian islands, in order to test their buoyancy, he would 

 obtain such a result as is given in this diagram. Two varieties of 

 the tree would be at once indicated, and further research would 

 indicate that these varieties were connected with littoral and inland 

 stations. This subject is further dealt v/ith in Chapter XVII. 



