216 DRY FARMING 



duction of seeds be prevented but the plants already 

 established must be killed. In the second column of the 

 tables in Sec. 174 the classification of our worst weeds 

 according to duration is indicated. 



173. Habits of Root Growth and Time of Seeding.— 

 In addition to knowing the "duration of growth" of 

 weeds, it is essential also to know the habit of root 

 growth of each, because on this point depends very 

 largely the nature of the means of eradication. 



There are three more or less distinct forms of roots, 

 (1) fibrous roots, (2) tap roots and (3) the so-called 

 "creeping roots" or underground stems. Annual weeds 

 usually have fibrous or tap roots, biennials generally 

 have tap roots while perennial weeds may have fibrous, 

 tap or creeping roots. The following are typical weeds 

 of each of these types: 



Fibrous rooted annual . . . Wild Oats. 



Tap rooted annual Lamb's Quarters and Most 



Mustards. 

 Tap rooted biennial Tansy Mustard and . Blue 



Burr. 

 Fibrous rooted perennial . Wild Barley. 

 Tap rooted perennial .... Curled Dock. 

 Creeping rooted perennial. Canada Thistle, Sow 



Thistle, Quack Grass. 



The creeping rooted perennials are the most difficult 

 to kill because of the fact that from each joint of the 

 so-called "roof there may be sent up new plants even 

 after tiie parent stem has been plowed down, 



174. How Weeds Spread. — Nature is the chief agency 

 in the spread of weeds but man is largely responsible 

 for the present condition of our cultivated fields. 



