DISSEMINATION OF SEEDS. 141 



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 oif ; and, when gaining the land, they would 

 be sure to fly to their natural fresh-water haunts." Darwin 

 tried several experiments to show that the mud of ponds 

 is charged with seeds, the most striking one being the 

 following: — "I took in February," he says, "three table- 

 spoonfuls of mud from three different points, beneath 

 water, on the edge of a little pond ; this mud, when dried, 

 weighed only six and three-fourths ounces. I kept it cov- 

 ered up in my study for six months, pulling up and count- 

 ing each plant as it grew. The plants were of many kinds 

 and were five hundred thirty-seven in number, and yet the 

 viscid mud was all contained in a breakfast cup ! Consid- 

 ering these facts, it would be an inexplicable circumstance 

 if water-birds did not transport the seeds of fresh-water 

 plants to unstocked ponds and streams situated at very 

 distant points." 



When considering birds as seed-carriers, the w succes- 

 sion of forest-trees," a ftubject about which much has been 

 written, is naturally suggested. When a forest springs 

 up naturally where none of its kind has been known to 

 exist, we do not hesitate to say that it sprang from seeds. 

 The lighter seeds, as maples and pines, were carried by 

 the wind ; the heavier, as nuts and acorns, by birds and 

 squirrels. When an oak wood is cut down, a pine forest 

 does not immediately spring up, unless in the neighbor- 

 hood there are pine trees. This is a view opposed to that 

 of many who suppose that in this and in similar cases the 

 trees of the new forest have sprung from seeds spontane- 

 ously produced, or which have lain dormant for hundreds 

 of years, or which may have been led to show signs of 

 life by heat from a fire. So, too, when a pine forest is 

 succeeded by an oak, the explanation is simple. Squir- 



