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Show [CnAP. XII. GEOGRAPHICAL DISTRIBUTION. 336 h same country. But two rapidly spread throughout J e d no doubt many others facts which I have observe -an e light on this subject. rema'·i n to b e ob serv ed-throw sfo mm a pond covere d WI' th Wh.en a duck suddenl~ emer:~he~e little plants adh~ring duck-weed, I have. twiCe se ened to me, in renlOVIng a to its back ; and It has happrium to another, that I have little duck-weed from one a~ud the one with fresh-water quite unintentionally stoB ~ another agency is perhaps shells from the I.th~r. au d a duck's feet, which might more effectual : su~pen 1 e in in a natural pond, in an represent those of a buds e:p ofg fresh-water shells were aquarium, where £anyd ~~at numbers of the extremely hatching ; a~d I h ~~hed shells craw led on the feet, and minute and JUSt fi a 1 that when taken out of the water clung to them so ~m Y d ff though at a somewhat more they could not be Jarre 1~ 'oluntarily drop ofl'. These advanced age theh wou tho:gh aquatic in their nature, just hatched mo us~s, £ t 'n damp air from twelve to survived on the dd~k ~h ~e l~~gth of time' a duck or heron twenty hours ; an ~n IS even hundred miles, and would tnight fly at least SIX or\ rivulet if blown across the be -sure to alig~t ?~ a j~~ t~rany oth~r distant point. Sir sea to an oceanic IS ~n that a Dyticus has been Charles ~yell a~o ulform(a sfr:~-water sheillike a limpet) caught Wlth ~n nc~;l.s d a water-beetle of the same f..i rm.l y adhering tot eIs ' onacne 1.tl1 ew on board the 'Bea~le,' family, a Colymb1 d' t t from the nearest land: lOW when forty-fiv~ mi ~s htish:.e flown with a favouring gale much farther 1t mig no one can tell. 1 t 't has long been known what With respect to p an sh, I t and even marsh-species enormous ranges m an. y fres -wd at ert he most remote oceam·c have, both over cont~n~nts an o as remarked by Alph. islands. This is strikingly show~~rrestrial plants, which de Candolle, in large groupt~ of mbers . for these latter have on1 y a very few aqu.a IC mief in con' sequence, a very seetn immediately ~o acf:•quire, ~le means of dispersal exwide range. I think avoura . d that earth occa-plain this fact. I hav 1 e b~he ;:ein_t1~:~e quantity to the sionally, though rare y, a er CHAP. XII.] FRESH-WATER PRODUCTIONS. 337 feet and beaks of birds. Wading birds, which frequent the muddY: edges of ponds, if suduenly ~ushed, would be the most hkely to have muddy feet. Buds of this order I can show are the greatest wanderers, and are occasionally found on the most remote and barren islands in the open ocean; they would not be likely to alight on the surface of the sea, so that the dirt would not be washed off their feet; when making land, they would be sure to fly to 'their natural fresh-water haunts. I do not believe that botanists are aware how charged the mud of ponds is with seeds : I have tried several little experiments but will here give only the most striking case: I took in February three table-spoonfuls of mud from three different points, beneath water, on the edge of a little pond; this mud when dry weighed only 6! ounces ; I kept it covered up in my study for six months, pulling up and counting each plant as it grew; the plants were of many kinds, and were altogether 537 in number; and yet the viscid mud was all contained in a breakfast cup ! Considering these facts, I think it would be an inexplicable circumstance if water-birds did not transport the seeds of fresh-water plants to vast distances, and if consequently the range ·of these plants was not very great. The san1e agency may have come into play with tlie eggs of some of the smaller fresh-water animals. Other and unknown agencies probably have also played a part. I have stated that fresh-water fish eat some kinds of seeds, though they reject many other kinds after having swallowed them ; even small fish swallow seeds of moderate size, as of the yellow water-lily and Potamogeton. Herons and other birds, century after century, have gone on daily devouring fish; they then take flight and go to other waters, or are blown across the sea ; and we have seen th~t seeds retain their power of germination, when r~jeoted in fellets or in excrement, many hours afterwards. Wb~n saw the great size of the seeds of that fine w;:tte:r~lily, th~ N elu:mbium, and remembered A~ph. ?e ~an?olle's remark~ on _thi~ plant, I ~ought that Its <hstnbutwn must remain qmte mexplica-le; but Audubon states that he found the seeds of the 15 |
