XIII ADAPTATION AND SEED-BUOYANCY - 125 



seeds almost an inch long of a huge pumpkin (Cucurbita) which, in 

 sound condition, form one of the commonest constituents of the 

 beach drift on the coast of Chile from Valparaiso northward to 

 Iquique. The fruit is commonly eaten by the lower classes. The 

 seeds, which are very buoyant, contain a kernel that does not 

 float, the buoyancy being due to the water-tight coats which, as 

 shown in the plate in Chapter XII., possess well developed air- 

 bearing tissues. It may here be observed that Martins refers to 

 the germination of seeds of Cucurbita pepo after 45 and 93 days' 

 flotation in sea-water. 



One sometimes finds buoyant tissue developed in the seeds of 

 bottle-gourds, where it can serve no useful purpose of dispersal. 

 Thus small bottle-gourds, seemingly of the genus Cucurbita rather 

 than of Lagenaria, are to be commonly found afloat in the Guay- 

 aquil River and stranded on the Ecuador beaches. They will float 

 for many months, and contain the seeds dried up into a small loose 

 compacted mass in their interior. These seeds, which contain a 

 layer of spongy air-bearing tissue in their coverings, will in several 

 cases float for months. Some that I had been keeping two months 

 afloat in sea-water germinated freely. It is shown in Note 47 that 

 bottle-gourds containing sound seeds are dispersed far and wide by 

 the currents. In some species the seeds are buoyant, and in others 

 they sink in sea-water ; but the gourds themselves will float for 

 probably a year or more, and the floating capacity of the seeds 

 when it exists is too insignificant to affect the fruit's buoyancy. 



Other instances of the useless buoyancy of fruits of inland 

 plants are afforded by different species of Citrus. In the floating 

 drift of the Fijian rivers the fruits of the wild and indigenous 

 Shaddock (C. decumana) and of an inedible Orange, also wild and 

 indigenous (C. vulgaris ?), are at certain times to be found, the 

 latter often in numbers. The first-named floats four to five weeks 

 in sea-water, and the last-named nearly two months, and both are 

 to be observed floating out at sea between the islands. The fruits 

 of the Tahitian Orange, a variety of C. aurantium, floated in sea- 

 water between three and four weeks. The seeds of these and 

 other species of Citrus sank in from a few hours to a day or two. 

 The buoyancy of the fruit depends on the rind — the thicker the 

 rind the greater the floating power. This was not only shown in 

 the length of the period of flotation, but also in the buoyant 

 behaviour of the fruit. With the Tahitian Orange, where the rind 

 is relatively thin, the fruits floated heavily in sea-water and only 

 protruded slightly above the surface. With the Shaddock and 



