CHAPTER IX 



PLANTS IN THEIR RELATION TO HUMAN WELFARE 



134. Introduction. Thus far in our study of plant biology 

 we have considered the principal functions carried on by 



FIG. 60. Sweet potato plant. 



plants and have observed some of the adaptations of struc- 

 ture for performing these functions. We have proved, for 

 example, that plants must feed, digest, breathe, and carry 



126 



