398 A NATURALIST IN THE PACIFIC chap. 



*' Ndambe-ndambe-ni-nga " and " Vothe-vothe-ni-nga," meaning 

 respectively "the duck's seat" and "the duck's paddle." 



CeratopJiylluvi demersum 



This wonderful aquatic has been dispersed over most of the 

 globe ; but I will only mention its occurrence in oceanic islands, 

 such as Fiji, Samoa, the Bermudas, and the Azores, to indicate 

 the necessity of attributing its distribution in islands to birds. 

 Several years ago I made a careful study in England of the 

 habits and mode of germination of this plant, the results of which 

 are given in Science Gossip for November, 1894 ; but reference can 

 only be made here to such points as bear on the occurrence of the 

 plant in the Pacific islands. 



It is well known that in our English ponds and rivers the plant 

 propagates itself, as a rule, by budding ; and that it is only in 

 unusually hot and dry summers, such as that of 1893, when many 

 ponds became very low and were excessively heated, that the fruits 

 mature in any quantity. My observations clearly showed that 

 a higher temperature is required for the completion of maturation 

 than for the early stage of the fruiting process and for the flower- 

 ing. After a comparison of my river and pond temperatures, I 

 formed the conclusion that whilst in water 12 to 18 inches deep 

 this plant requires for a week or more an average daily maximum 

 water temperature of 70° F. to produce its flowers, a warmth of 

 80' and over is necessary to mature its fruit, a condition to be 

 found in England only in shallow ponds, where the plants may 

 fruit abundantly, but not in rivers, where they flower and rarely 

 mature the fruit (see also for the thermometric conditions my 

 paper in Proc. Roy. Phys. Sac. Edin., xii, 296). Since a yet lower 

 temperature (an average maximum water temperature of 6^° for 

 a week or more) is sufficient for germination, it follows that 

 the thermal conditions of our English climate will allow Cerato- 

 phyllum to germinate and to flower, though but rarely to mature 

 the fruit. 



Even in Fiji we can notice the distinction between the cooler 

 river and the superheated ponds and swamps of the Rewa delta as 

 regards the maturation of the fruit. In 1897 I found Ceratophyllum 

 thriving in the main channel of the Lower Rewa where the water 

 was quite fresh ; whilst lower down where the water was often 

 brackish its place was taken by Ruppia maritima. In the main 

 river, where the water unmixed with sea-water rarely acquires 



