AS AN AGENT IN PLANT DISPEBSAL. 341 



with the drift of these rivers, I pa-s on to remark on its negative 

 character, as indicated in the absence of the seeds and seed- 

 vessels of most of the familiar water-plants that flourish in their 

 waters, a suggestive fact when we remember the wide distri- 

 bution of these plants. In other words, we find in the drift the 

 seed-vessels and seeds of the plants that live on the banks rather 

 than those of the plants that live in the water. One misses, 

 with two or three exceptions, the nuts of the Potamogetons. We 

 find none of the seeds of the yellow and white Water- Lilies, 

 NupJiar luteum and Nymphcea alba. Not even the nuts of the 

 Water-Persiearia (Polygonum ampTiibium) are to be seen. Nor 

 do the fruits of the Water- fianuncul us (ifoww/iewZj/s aquatilis) or 

 of the Water Forget-me-not {Myosotis palustris) come under our 

 notice. Where are the fruits of Ceratophyllum demersum and the 

 nuts of Scirpus lacustris, plants that are common enough in 

 places in these rivers ? The missing seeds and seed-vessels I 

 find by my experiments to have little or no floating-power 

 either in a river or in the sea : they are to be found lying in the 

 river-mud. 



I will take, first, the case of Scirpus lacnstris. Even if the 

 nuts are kept dry for eighteen months, they will not be able to 

 float more than a day or two, and the terminal tufts of spikelets 

 give no aid in transport. And yet we have here a plant that 

 is found all over the globe. As far as I can judge at present, 

 Scirpus nuts, as a rule, sink (for instance, those of Scirpus pa- 

 lustris sink like a stone) ; and thus they differ strikingly from 

 the fruits of the Carices, which can often float a winter through, 

 though owing their buoyancy entirely to the utricle* Tiiere is, 

 however, an exception in the case of the sinking of the Scirpus 

 nuts, those of Scirpus maritimus floating some time, a circum- 

 stance that may perhaps explain its station. However this may 

 be, I will return to the question of Scirpus lacustris. It is 

 found everywhere, and can get by water nowhere ; and we aro 

 driven to find an explanation of its wide distribution in the 

 agency of birds. Basing his conclusion on, as I infer, similar 

 grounds, Mr. Hemsley, in bis account of the Flora of the 

 Bermudas, attributes its dispersal to birds. Wild duck probably 

 aid in the dispersal of this plant as well as of others of the widely- 

 spread species of Scirpus. As yet, I have only examined 

 four of these birds, and three oi them contained in their 

 gizzards the nuts of Scirpus or of other genera of Cyperaceae. 



