926 ECOLOGY 



the peanut and in the fruits of the cleistogamous flowers of Polygala 

 (fig. 1 191) and Viola; though this habit might seem disadvan- 

 tageous, no seeds are better placed for germination. A vast number 

 of seeds and fruits have no regular means of dispersal apart from drop- 

 ping to the ground beneath the plant that bore them; among such are 

 the nuts, the acorns, and many other heavy fruits or seeds. Scarcely 

 more eflfective are the numerous cases of mechanical propulsion from de- 

 hiscent fruits. However, in all these cases the seeds are likely to lodge 

 in places that are relatively fit for germination. 



The effective agents of distant dispersal are water, wind, and animals. 

 Water probably is the most likely to carry disseminules for great dis- 

 tances, but the number of seeds which fall into the water is limited; a 

 great many of these seeds also are injured in transit, and still more fail 

 to lodge in a suitable habitat. Water, however, is of the utmost impor- 

 tance as a transporter of the fruits and seeds of plants which grow in 

 the water, or in swamps, and along shores, since deposition is likely to 

 be in a place that is fit for subsequent growth.^ Temporary streams, 

 such as torrents following heavy rains, and permanent streams in times 

 of flood, are highly important agents in the dispersal of the seeds of land 

 plants. Wind is the most likely of all agents to pick up and transport 

 seeds and fruits in great numbers from all habitats, but it is also the most 

 indiscriminate of scatterers, depositing all kinds of seeds in all kinds of 

 places, so that the waste of disseminules is enormous. Seeds and fruits 

 scattered by animals may or may not be carried far, but they are likely 

 to lodge in a favorable situation, since animals of a given species tend to 

 frequent similar habitats; wading birds, for example, fly from swamp 

 to swamp, and grazing animals scatter hooked fruits in places similar 

 to those in which they were gathered. 



Probably, in spite of its wastefulness, wind is the most efficient of dis- 

 persing agents. On newly formed islands the pioneer plants of the in- 

 terior portions are mainly those whose disseminules are scattered by 

 wind, a smaller number being scattered by birds, while the shore plants 

 are brought largely by water currents. For example, on the island of 

 Krakatoa, whose vegetation was entirely destroyed by a volcanic eruption 

 in 1883, the first plants were thallophytes and bryophytes with wind- 

 bome spores, and the first higher plants to reappear in abundance were 



' However, the water may carry seeds so far that the new climate is unsuited for de- 

 velopment, as in the West Indian seeds carried to the shores of Norway by the ocean 

 currents. 



