.85. NOTES AND COMMENTS. 725 



instance, in Rnmcx congloiiieratits, but in the case of Raiiuncuhis repens and 

 aquatilis the process is often permanently checked. Some seedlings 

 will develop the first leaves during the daily thaw, while locked in the 

 ice at night. 



The seeds and fruits of the river drift will, almost without excep- 

 tion, float for months in sea-water, and afterwards germinate. Fruits 

 of Sparganium rainosum germinated after being afloat in sea-water for 

 a year, and those also of many others after periods of from three to 

 five months, the limit not of their buoyancy but of the experiment. 

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

 loss of germinating power of the seed ; on the contrary, it sometimes 

 favours the process, as the sinking is due to loss of vitality of the 

 outer coverings on which the buoyancy of the fruit nearly always 

 depends, and the decay of these coverings is often a necessary step 

 to germination. Thus nuts of Potamogeton natans, which float for 

 months in fresh-water, sink after a week or two in sea-water ; until 

 they are ready to sink they cannot germinate, so that sea-water 

 quickly accomplishes what may take months in fresh-water. 



As regards seeds already germinating that may reach the sea, in 

 those of Rumex the process is arrested, and the protruding part of the 

 radicle rots off" ; but if after a week or two fresh-water is again reached, 

 the process is recommenced, and an undersized seedling prematurely 

 discharged, which, hovv-ever, soon recovers, and develops the plumule. 

 In the yellow flag the radicle soon rots off, and germination is not 

 continued when the seed is restored to fresh-water. Rarely is the 

 germinating seed but little aff'ected, as in Ranunculus scelerafus, which 

 will germinate in sea-water. 



As regards seedlings, some such as the yellow water-lily, the 

 water-plantain, and Mentha aquatica, are killed by sea-water in a day or 

 two and sink. Others will float for a week or ten days and yet 

 recover, though often much mutilated. The seeds of Salicornia lierhacea 

 sink even after a winter's drying, yet they germinate freely, and the 

 seedling rises to the surface and thrives. 



Mr. Guppy remarks on the absence in the river-drift of the seeds 

 and seed-vessels of most of the familiar water-plants ; in fact, we find 

 represented the plants that live on the banks rather than those 

 of the water. With two or three exceptions the nuts of the pond- 

 weeds are absent, as are the seeds of the yellow and white water- 

 lilies, the fruits of the forget-me-not [Myosotis palustris), the water 

 ranunculus {R. aquatilis), and even the nuts of Polygonum amphibiiim. 

 Nor do we find the fruits of the horn wort [Cevatophyllum demci'sinn) or 

 the nuts of the bulrush {Scirpus lacnstris). The missing seeds and 

 fruits, however, have little or no floating power either in river or sea, 

 and must be sought in the river mud. Now these plants have a very 

 wide distribution, many being universal in fresh-water ponds and 

 rivers, and yet they cannot of themselves cross the sea. It is to birds 

 that we must look for the dispersal of many of our water-plants, 



