650 



WEED FLORA OF IOWA 



Fig. 510. Biennial root of Young Bull Thistle (Cirsium lanceolatum) after one 



year's growth. 

 (Photographed by Charlotte M. King.) 



food are stored in the roots. The same is true of the perennials 

 although to a less marked degree than of the biennials. 



By studying the root system in the late fall we may determine 

 roughly whether the weed is an annual, a biennial or a perennial. 

 That is to say, dead small fibrous or primary roots and seed produc- 

 tion indicate an annual ; large fleshy roots and no seed production 

 a biennial; reserve food within the roots beside seed production a 

 perennial. 



PROPAGATION OF WEEDS BY ROOTS AND STEMS. 



Prof. Hitchcock says that weeds may be propagated by seed and 

 buds or by vegetative sprouts. The layman is inclined to call all 

 parts of the plant below ground root. It may be, however, a stem 

 called a root-stock or rhizome. Microscopical examination is often 

 necessiary to determine which is root and which is stem. 



