176 FRESH-WATER PRODUCTIONS. [Chap. XIIL 



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 many hours 

 afterwards in pellets or in the excrement. "When I saw 

 the great size of the seeds of that fine water-lily, the Ne- 

 lumbium, and remembered Alph. de CandoUe's remarks 

 on the distribution of this plant, I thought that the means 

 of its dispersal must remain inexplicable; but Audubon 

 states that he found the seeds of the great southern 

 water-lily (probably, according to Dr. Hooker, the Ne- 

 lumbium luteum) in a heron's stomach. Now this bird 

 must often have flown with its stomach thus well 

 stocked to distant ponds, and then getting a hearty 

 meal of fish, analogy makes me believe that it would 

 have rejected the seeds in a pellet in a fit state for 

 germination. 



In considering these several means of distribution, it 

 should be remembered that when a pond or stream is 

 first formed, for instance, on a rising islet, it will be 

 unoccupied; and a single seed or egg will have a good 

 chance of succeeding. Although there will always be a 

 struggle for life between the inhabitants of the same 

 pond, however few in kind, yet as the number even in a 

 well-stocked pond is small in comparison with the num- 

 ber of species inhabiting an equal area of land, the 

 competition between them will probably be less severe 

 than between terrestrial species; consequently an in- 

 truder from the waters of a foreign country would have 

 a better chance of seizing on a new place, than in the 

 case of terrestrial colonists. We should also remember 

 that many fresh-water productions are low in the scale 

 of nature, and we have reason to believe that such be- 

 ings become modified more slowly than the high; and 



