Dispersion of Fruits and Seeds. 215 



wind across open spaces, the seeds being scattered from 

 their pods during the journey. It is this tumbhng habit 

 which helps to make the Russian thistle such a troublesome 

 pest. 



147. Dispersion by Birds. — The birds are the most effec- 

 tive agents among animals for distributing seeds. They 

 often swallow berries and other pulpy fruits whose seeds 

 are too small or hard to be broken up in the gizzard, and 

 are finally ejected undigested and capable of germination. 

 Such berries are usually inconspicuous and unpalatable 

 until the seeds are ripe, when they take on bright colors, 

 are often fragrant, and their pulp becomes agreeable to the 

 taste, with the evident design of attracting those animals 

 which may aid in scattering the seeds. 



Small seeds are often carried from place to place while 

 embedded in the mud clinging to the feet of birds and other 

 animals ; thus Darwin found that eighty-two seeds germi- 

 nated from the mud taken from the feet of a single par- 

 tridge. The small floating seeds of water plants often 

 cling to water fowl as they rise for flight, and are carried 

 to other waters. Those birds which are able to sustain 

 swift and prolonged flight must be particularly efficient in 

 scattering seeds over broad areas. Pigeons and cranes, 

 for instance, can fly about forty miles per hour, and swal- 

 lows and peregrine falcons can cover a hundred miles in the 

 same length of time. 



148. Dispersion by Other Animals. — Seeds of various 

 plants are carried away and stored by squirrels and other 

 animals. Most of these seeds are doubtless eaten, but 

 some of them are dropped in transit. In such cases the 

 service of carriage seems to be dearly paid, but we may be 

 sure the expense is not unwarranted, since nut-bearing 

 trees and shrubs have been able to maintain themselves 



