AS AN AGENT IN PLANT DISPERSAL. 313 



hours, some 1600 or 1700 seeds rise to the surface, where they 

 float in a mass which, on account of the gelatinous aril in- 

 vesting each seed, looks like a patch of fish-spawn. During its 

 day or two of flotation this would doubtless often attract birds. 

 There are many interesting matters relating to these plants, 

 when viewed from the standpoint of their dispersal, to which I 

 cannot here refer. However, I should remark that, curiously 

 enough, the seeds of Nuphar luteum, after drying some weeks, 

 are able to float several weeks in sea-water, though their buoyancy 

 in fresh water is not much increased. But the seeds kept floating 

 in sea-water have not yet germinated ; and if they do, it is 

 doubtful whether in such an experiment we are at all imitating 

 the process Nature adopts in the dispersal of these plants. 



Lastly, I come to the Potamogetons of these rivers, many of 

 which are found all over the globe. Most of them present little 

 or no facilities for their dispersal by sea. Take, for instance, Po- 

 tamogeton densus. Its fruits sink at once both in fresh and salt 

 water, and yet the plant frequents Europe, Asia, and America. 

 The same may be said of the fruits of Potamogeton obtusifolins, a 

 plant very widely distributed. The nuts of Potamogeton perfo- 

 liatus will not float more than a week or two in the sea, though 

 floating often several weeks in fresh water ; and yet this plant, 

 as I learn from Bentharn and Hooker's ' Handbook,' is found all 

 over the northern hemisphere, and even in Australia. These 

 plants, by their floating shoots and portions of their stems, dis- 

 perse themselves in rivers ; and from these materials found 

 floating in the river-drift in the spring I have raised plants. But 

 they present little or no capacities for sea transportal ; we must 

 therefore attribute their dispersal to birds. 



These examples will, I think, be sufficient to illustrate my 

 argument that for the dispersal of many of our water-plants we 

 must look to birds ; and it would seem that birds adopt a more 

 systematic plan of stocking distant rivers and ponds with the 

 same plants than that with which they are usually credited. This 

 is not a strictly botanical matter, but rather a subject for ordinary 

 observation. Giving my opinion for what it is worth, I should 

 be inclined to consider that the seeds and fruits of many water- 

 plants are more frequently transported in the digestive canal 

 of a bird than in mud sticking to its feet or plumage. The 

 Scirpus nuts that germinated after being taken from the gizzard 

 of a wild duck must have been originally sifted out of the river- 



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