Chap. XIII.] FRESH-WATER PRODUCTIONS. 175 



feet and beaks of birds. Wading birds, which frequent 

 the muddy edges of ponds, if suddenly flushed, would be 

 the most likely to have muddy feet. Birds of this order 

 wander more than those of any other; and they are 

 occasionally found on the most remote and barren 

 islands of the open ocean ; they would not be likely to 

 alight on the surface of the sea, so that any dirt on their 

 feet would not be washed off; and when gaining the 

 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 dried weighed only Q^ 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 cir- 

 cumstance if water-birds did not transport the seeds 

 of fresh- water plants to unstocked ponds and streams, 

 situated at very distant points. The same agency may 

 have come into play with the 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 

 33 



