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Show BUTION CHAP. XII. 386 GEOGRAPHICAL DISTRI • . f th t a Dyticus has been caught with an In orms me a 1. t) fi 1 d Ancylus (a fresh-water shell like a Impe rm ~ a - h . t .t. and a water-beetle of the same family, a enng o I , , B 1 ' h Colymbetes, once flew on board the . eag e, .w en forty-five miles distant from the .nearest la~d. how much farther it might have flown with a favounng gale no one can tell. With respect to plants, it has long been known what enormous ranges many fresh-water and even marsh ... species have, both over con~in~nts ~~d to the most remote oceanic islands. This IS strikingly shown, as remarked by Alph. de Candolle, in large groups ?f terrestrial plants, which have only a very few aquatic members· for these latter seem immediately to acquire, as if in c~nsequence, a very wide range. I think favourable means of dispersal explain this fact. I have before mentioned that earth occasionally, though rarely,. adheres in some quantity to the feet and beaks of birds. Wading birds which frequent the muddy edges of ponds, if sudd~nly flushed, would be the most likely to have muddy feet. Birds of this order I can show are the greatest wandGrers, and are occasionally found on the most remote and barren islands in the open ocean ; they would not be likely to alight on the surfac~ of th~ sea, so that the dirt would not be washed off theu fee~, when making land, they would be sure to fl~ to thelf natural fresh-water haunts. I do not beheve th~t botanists are aware how charged the mud of ponds IS with seeds: I have tried several little experiments, b~t will here give only the most striking case : I took ~n February three table-spoonfuls of mud from three . chfferent points, beneath water, on the edge of a httl~ pond· this mud when dry weighed only 6£ ounces~ kept 'it covered up in my study for six months, pulling up and counting each p1a nt as 1't grew; the plants were CHAP. XII. FRESH-WATER PRODUCTIONS. 387 of many kinds, and were altogether 537 in numb .. and ,y et the viscid mud was all contained in a b k.!'er t' 0 'd . rea 1as cup. onsi enng these facts I think it would b 1. nexp lI'C a ble cr. rcumstance if wa' ter-birds did not trea nasn-port the seeds of fresh-water plants to vast di t d if s ances, an consequently the range of these plants was not very g.reat. The same agency may have come into pl~y With the eggs of some of the smaller fresh-water animals. Other and unknown agencies probably have also played~ part. I have stated that fresh-water fish eat s~me kinds of ~eeds, though they reject many other kinds after hav1ng swallowed them; even small fish s:wallow seeds of moderate size, as of the yellow waterhly 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 that seeds retain their power of germination, when rejected in pellets or in excreme;nt, many hours afterwards. When I saw the great s~ze of the seeds of that fine water-lily, the N elumbium, and remembered Alph. de Candolle's remarks on ~his plant, I thought that its distribution must remain quite inexplicable; but Audubon states t~at he found the seeds of the great southern waterlily (pro~ably, according to Dr. Hooker, the N elumbium luteum) m a heron's stomach; although I do not know ~h~ fact, yet analogy makes me believe that a heron ymg to another pond and getting a hearty meal of fish, ~~uld probably reject from its stomach a pellet conta1nmg the seeds of the N elumbium undigested · ~r ~he .seeds might be dropped by the bird whilst eedin~ Its young, in the same way as fish are known som~times to be dropped. In considering these several means of distribution, s2 |