SEEDS AND FRUITS 171 



of the seeds produced annually are used 

 as food, yet enough are preserved to 

 perpetuate the species, so that this plant 

 is represented by many millions of in- 

 dividuals in regions where it would 

 have none if it were not for man. 

 Thus without the interference of man 

 corn could not grow and seed from year 

 to year in any place in northern United 

 States. 



214. The fruit of the dot-bur, Xanihium. The 

 fruits of this plant, which is a relative of the sun- 

 flower, are very much different from those previously 

 examined, both in structure and action. The plant 

 is a weed, and it is more or less abundant over a 

 great part of the United States. The fruits may 

 be taken from the plant in August or September, 

 picked up from the ground or taken from the coats 

 of animals in late autumn. 



I. External appearance of fruit. 



Examine the clusters of four or five fruits, and 

 note their position on the plant as well as 

 the following features : 

 a. The prongs at the apex, and the hooked 



