ROOTS AND ROOT-STOCKS OP WEEDS 



649 



Fig. 509. Fibrous roots of Buckhom. 

 (Photographed by Gardner.) 



docks and wild morning-glory. These plants do not, as a rule, 

 produce large quantities of seed but depend upon the roots or 

 stems as a means of propagation. Thus if a field infested with 

 quack grass or morniug-glory is plowed or disked the roots or 

 rhizomes are broken up and each piece may produce a new plant. 



Some roots which do not spread extensively through the soil but 

 form new plants from offshoots from the crown, such as the docks 

 and wild gourds, form heavier roots from year to year for the fol- 

 lowing reason: The root growth is most active at the apex of the 

 main roots. This resumption of growth starves many of the older 

 roots, as we find few lateral on these older portions, and it thus 

 extends the root system. 



In the annuals there is little need for a large amount of reserve 

 food within the roots for the elaborated food is used up largely as 

 it is manufactured. The life of the plant ceases when seed is 

 produced. In the biennials, however, large quantities of reservo 



