AS AN AGENT IN PLANT DISPERSAL. 339 



seem to get fresh vigour in the ice, and, like those of Ranunculus 



aquatilis and Rhinanthus Crista-galli, will even develop the first 



leaf or leaves during the daily thaw, whilst locked in the ice at 

 night. 



I pass now to the consideration of those seeds and seed-vessels 

 which reach the sea. There is scarcely one of the seeds and 

 seed-vessels common in the drift of the Lea and the Thames 

 that will not float for months in sea-water and afterwards germi- 

 nate. Fruits of Sparganium ramosum germinated after as much 

 as twelve months afloat in sea-water ; and those of Ranunculus 

 repens, Ranunculus sceleratus, Galium palustre, Bidens sp., 

 Lycopus europceus, Scutellaria galericulata, Mentha aquatica, 

 Atriplex patula, Rumex conglomerate, Alisma Plantago, Iris 

 Pseudacorus,&c, with different species of Carex, such as C. vulpina 

 and C. Pseudocyperus, germinated after periods of flotation of 

 from 3 to 5 months, which were the limits not of their buoyancy 

 but merely of my experiments. Mr. Hemsley treats at length of 

 these matters in his work on the Botany of the 4 Challenger ' 

 Expedition, a volume which has been an endless source of inspi- 

 ration to me in many ways, and I cannot do more than touch on 

 the fringe of the subject here. However, I may remark that 



many seed-vessels that will withstand sea-water will germinate 

 also after a prolonged immersion in water of a much greater 

 salinity. Those of Sparganium ramosum, Carex Pseudocy 



leru 



Scirpus maritimus, &q. will germinate after an immersion of 

 months in sea- water, the density of which has been raised to 

 1*050 by the addition of salt. The tiny seeds of Juncus com- 

 munis readily germinate after lying a long time in ordinary sea- 

 water ; on the other hand, the seeds of the Lemnce, if those of 

 Lemna minor may be taken as a sample, will only suffer a few 

 days' flotation in sea-water. 



The sinking of a seed-vessel in sea-water by no means involves 

 the loss of the germinating-power of the seed. A fruit of Spar- 

 ganium ramosum that sank after floating 11 \ months in sea- 

 water afterwards germinated ; and most of the fruits of Galium 

 palustre that sank during my sea-water experiments on that 

 plant aho germinated ; and I might give other instances. Sea- 

 water causes the sinking of fruits by affecting the vitality of 

 the outer coverings, on which the buoyancy of fruits nearly 

 always depends. We see this especially well in the case of the 

 nuts of Potamogeton natans, which, whilst they float some months 



