AUTUMN WINDS AND WINTER FLOODS 281 



ing the vessel under the air-pump, all the seeds 

 without exception sank after twenty-four hours." The 

 long-continued flotation of Alder-nuts is therefore to 

 be attributed to the numerous air-tight compartments 

 of the wall or shell, and to the oily matter which 

 renders them incapable of wetting. We shall shortly 

 see that both precautions are employed in the case of 

 another fruit which is dispersed by water. 



I next turned to Dr. H. B. Guppy's paper on the 



FIG. 69. Part of the porous husk of an Alder-nut, highly magnified The dark 

 spaces are filled with air. 



River Thames as an agent in plant-dispersal, 1 which 

 contains many curious facts. He tells us, as the 

 result of his long-continued and laborious enquiries, 

 that not only in autumn but in winter and spring the 

 rivers carry down much vegetable drift. It is not 

 usually swept down at once to the sea. Winds 

 blowing across the river set up a surface-flow, by 

 which the drift is often lodged among the reeds or 

 embayed in sheltered creeks. Floods throw the drift 

 upon the banks, where it may rest for weeks and 

 months until another flood picks it up. Eddies detain 

 1 Journ. Linn. Soc., Botany y Vol. XXIX., p. 333 (1893). 



