APPENDIX 571 



It is scarcely likely that a seed-carrying gourd stranded on a beach 

 would be able to establish the plant without the aid of man ; but it seems 

 highly probable that gourds have often been introduced into new countries 

 by the currents and that man has afterwards cultivated them. These 

 plants may be contrasted with that remarkable Cucurbit, Luffa insularum, 

 a genuine littoral plant, the seeds of which, and not the fruits, are dispersed 

 in the Pacific by the currents (see page 426). 



NOTE 48 (page 126) 



On the Useless Dispersal by Currents of the Fruits of the 

 Oak (Quercus robur) and other Species of Quercus, and 

 also of the Hazel (Corylus avellana) 



The fruits of different species of Quercus are of not infrequent 

 occurrence in the seed-drift both of the temperate and tropical regions, 

 being brought down by the rivers to the sea and then stranded on the 

 neighbouring beaches. They were amongst the drift gathered by 

 Mr. Moseley in the open sea, 70 miles off the New Guinea coast (Bot. 

 Chall. Exped., iv., 294). I found them on the beaches of Keeling Atol! 

 where no oak exists, and on the beaches of the south coast of Java ; 

 whilst Prof. Schimper noticed them among the stranded drift of the Java 

 Sea, and Prof. Penzig found them stranded on the shores of Krakatoa. 

 They also came under my notice on the Sicilian beaches and on the 

 Italian coast at Cumas. Those of Quercus robur are to be found on the 

 English beaches and in the autumn drift of the Thames, but they soon 

 sink and disappear from river-drift. They are referred to by Dr. Sernander 

 as frozen with other floating seeds in the ice of the Scandinavian rivers ; 

 but he evidently does not regard them as possessing much independent 

 floating power. 



Some years ago the author made a number of experiments on the 

 buoyancy of the acorns of Quercus robur, and he formed the conclusion 

 that when freshly collected not more than 4 to 8 per cent, of mature fruits 

 will float in fresh-water, and not more than about 10 to 12 per cent, in sea- 

 water, but that in either case they all sink in a day or two. Immature acorns 

 float much longer, and it is these that mostly figure in the drift. However, 

 unlike most fruits of little- initial buoyancy the mature fruits gain consider- 

 able floating power by drying. Of some that had been kept for seven 

 months 20 per cent, floated after four weeks in sea-water and 1 5 per cent, 

 after 10 weeks. ... It may be added that, according to Thuret, the fruits 

 of Quercus ilex have little or no floating power. 



The buoyancy of the fruits of Quercus is due entirely to the cavity left 

 by the shrinking of the kernel. I never remember to have found one with 

 a sound seed amongst the drift in England and Sicily ; and I should doubt 

 much whether those in the tropical drift retain their germinating powers. 



