SEED DISPERSAL. 



461 



thus exposed. TJie dark brown achenes stand over the surface of the recep- 

 tacle, each one tipped with the long slender beak of the ovary. The "pap- 

 pus," which is so abundant in many of the plants belonging to the composite 

 family, forms here a 

 pencil-like tuft at the 

 tip of this long beak. 

 As the involucral bracts 

 dry and curve down- 

 ward, the pappus also 

 dries, and in doing so 

 bends downward and 

 stands outward, brist- 

 ling like the spokes of 

 a small wheel. It is an 

 interesting coincidence 

 that this takes place 

 simultaneously with 

 the pappus of all the 

 seeds of a head, so 

 that the ends of the 

 pappus bristles of ad- 

 joining seeds meet, 

 forming a many-sided 

 dome of a delicate and 

 beautiful texture. This 

 causes the beaks of the 

 achenes to be crowded 

 apart, and with the 

 leverage thus brought to 

 bear upon the achenes 

 they are pried off the 

 receptacle. They are 

 thus in a position to 

 be wafted away by the 

 gentlest zephyr, and 

 they go sailing away 

 on the wind like a 

 miniature parachute. 

 As they come slowly 



to the ground the seed Fig - 483- 



,. Lactuca scariola. 



is thus carefully low- 

 ered first, so that it touches the ground in a position for the end which 

 contains the root of the embryo to come in contact with the soil. 



