GEOGRAPHICAL DISTRIBUTION 347 



With respect to plants, it has long been known what 

 enormous ranges many fresh -water and even marsh- 

 species have, both over continents and to the most 

 remote oceanic islands. This is strikingly shown, as 

 remarked by Alph. de Candolle, in large groups of 

 terrestrial plants, which have only a very few aquatic 

 members ; for these latter seem immediately to acquire, 

 as if in consequence, 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 suddenly flushed, would be the 

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

 can show are the greatest wanderers, and are occa- 

 sionally 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 alto- 

 gether 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 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 



