76 A TEXT-BOOK OF GRASSES 



cum (L.) Karst., T. officinale Weber.) is a familiar exam- 

 ple of this group. Cutting off the plant below the crown 

 does not destroy the dandelion, as adventitious buds may be 

 produced on the cut root from which new shoots develop. 



102. Perennial weeds with creeping rhizomes or creep- 

 ing propagating roots include the most troublesome 

 species, as the widely spreading rhizomes or roots are 

 difficult to remove completely from the soil. Portions of 

 the rhizomes remaining in the soil may give rise to new 

 shoots. Creeping propagating roots are to be distinguished 

 from creeping rhizomes or rootstocks, which are modified 

 stems. Creeping roots possess no scales or modified 

 leaves, but have the structure of roots. They will, how- 

 ever, if they are propagating roots, have the power to 

 produce adventitious buds. Some weeds with creeping 

 roots are bindweed (Convolvulus arvensis L.) and sheep 

 sorrel (Rumex Acetosella L.). None of the weedy grasses 

 possesses creeping roots. Creeping rhizomes indicate 

 their character as modified stems by the presence of scales 

 that mark the nodes at regular intervals. To this group 

 belong the white morning-glory (Convolvulus Sepium L.), 

 the nut-grass (Cyperus rotundus L.) and Johnson-grass. 



103. Weedy grasses. — Grasses may be of all degrees 

 of weediness. Many species that are classed as weeds are 

 harmless since they are found only in waste places or 

 along roadsides. Among these are goose-grass, crowfoot- 

 grass and old-witch grass. Only a few of the more impor- 

 tant weedy grasses will be mentioned here. 



104. Annual weeds. — In the eastern states the com- 

 mon species are green foxtail, yellow foxtail, and upon 

 sandy land, the sandbur. Here, and more especially in 

 the South, crab-grass is a common weed. All these yield 

 readily to cultivation. Crab-grass is particularly trouble- 



