ROOTS AND ROOT-STOCKS OF WEEDS 651 



Pig. 511. Underground rhizomes of common Morning-glory (Convolvulus 



sepium). 

 (Photographed by Stevens.) 



Roots. 



Adventitious buds are produced at indefinite points along the 

 roots and from them stems and plants develop. A number of our 

 noxious weeds are propagated by these running or creeping roots, 

 such as: milkweed {Asclepias comuti), bindweed (Convolvulus 

 arvensis), sheep sorrel (Rumex acetosella), Indian hemp (Apocy- 

 num ccmnabinum) , perennial ragweed (Ambrosia psilostachya) , 

 pasture thistle (Cirsium undulatum) . 



The weeds mentioned above are comparatively shallow rooted. 

 A few weeds are propagated by buds which come from deep vertical 

 roots. Among them we find the following: horse nettle (Solanum 

 carolinense) , ground cherry (Physalis sp.), Canada thistle (Cirsium 

 arvense). 



Underground Stems or Rhizomes. 



These underground stems are usually found at a short distance 

 beneath the surface. Along these stems are found nodes with leaf 

 scales at definite intervals. From these nodes roots develop which 

 penetrate the soil and leafy stems which develop above ground. 

 Some of the weeds so propagated are as follows: quack grass 



