644 



WEED FLORA OF IOWA 



The pictures shown here are of plant roots obtained by the 

 first method, the wire cages being omitted. 



The roots of weedy plants vary widely in form, structure, and 

 in longevity. Their function is three- and sometimes fourfold: 

 First, to absorb water and dissolved mineral matter; second, to 

 ajiehor the plant in the soil; third, to act as a storehouse for re- 

 serve food, and fourth, may serve to propagate the plant. 



FiQ. 505. Eoots of VThite Sweet Clover (Melilotus alba). Plants with several 



strong branching roots. 



(Photographed by Stevens.) 



ROOT FORMS. 



Boot forms may be divided into four general types: First, the 

 primary; in this case a single, usually enlarged central root is de- 

 .veloped. From it grow the smaller lateral roots. The burdock 

 (Arctium lappa), is of this class. Second, multiple primary, 

 in which the embryonic root almost immediately breaks up into 



