How Plants Secure Change of Location 387 



method more effective is available. This method, in brief, is 

 this, — the provision of appliances which ensure that the seeds 

 shall be carried away by moving agencies that exist in the world 

 around. These agencies are principally three, — winds, water- 

 currents and animals. There is also a fourth, — gravitation, — 

 but it acts in a profitless direction, although indirectly it con- 

 tributes some aid to dissemination by making round seeds roll 

 down slopes, and causing elastically-walled heavy seeds, such as 



Fig. 154. — A pod of a poppy, showing 

 openings for exit of the seeds. 



Fig. 155.- 



-A fruit of Clover, showing the 

 hygroscopic hairs. 



many trees have, to rebound from hard surfaces with a force 

 which must oftentimes remove them considerably away from the 

 plant that produced them. The other three agencies, however, 

 are vastly important in dissemination, as the following descrip- 

 tions will amply attest. 



4. Waftage by Winds. — Of the motive forces of nature, winds 

 are one of the most ubiquitous, and the easiest of all for plants 

 to make use of. They occur in all grades from the wildest of gales, 

 creating disturbance through hundreds of miles, down to the 

 faintest of zephyrs confined to a limited region; and they include 

 as well those upward currents of air which rise over heated places 

 in summer to a height where wide-ranging breezes prevail. To 

 utilize these winds for their spread, plants have only to attach 



