FRUITS 



59 



spread of some of our worst weeds in this way. The burdock and 

 clotbur are familiar examples. In both the mass of little hooks is all 

 that remains of an involucre. Thus the whole fruit cluster may 



be carried about and seeds scattered. 

 In many other fruits of the compos- 

 ites, as in the cockleburs and beggar's 

 ticks, the whole fruits are provided 

 with strong curved projections which 

 The cockiebur. bear many smaller hooklike barbs. 



Fxamine the front of a cockiebur or a beggar's tick with a low magnifica- 

 tioii or even a hand lens. Draw such a fruit. Of what probable use are the 

 many barbs? 



Pappus. — Probably the most important adaptations for dis- 

 persal of seeds are those by which the fruit is fitted for dispersal 

 by the wind. That much-loved and much-hated weed, the dande- 

 lion, gives us an example of a plant in which the whole fruit, an 

 achene, is carried by the wind. The parachute, or pappus, is an 

 outgrowth of the ovary 

 wall. Many other 

 fruits, notably that of 

 the Canada thistle, 

 are provided with the 

 pappus as a means of 

 getting away. If dan- 

 delions are available, 

 notice the wonderful 

 lightness and strength 

 of the pappus. In the 

 milkweed the seeds 

 have developed a silky 

 outgrowth which may 

 carry the seeds for 

 miles. In New York 

 city the air is some- 

 times full of the down from these seeds which is brought from 

 far over the meadows of New Jersey by the prevailing westerly 

 wind. 



Dandelion heads; the middle one a ma.ss of ripe fruits ready 

 to be scattered by the wind. Photographed by Overton. 



