Plants supply man with food,clothing,and shelter his most important need. many of our most useful medicines are also make from enjoy the smell of flowers, the sigth of a field of waving grain, and the quiet of a forest.Not all plants are helpful to man. some species grow in fields and gardens as weeds that choke off useful plants. Tiny bits of pollen from certain plants cause such diseases as asthma and hey fever. Other plants destroy millions of dollars worth of crops yearly.